REPORT ON THE POTENTIAL SOURCE OF THE INSECT BITES FOUND ON STUDENTS AT CLIFFORD ELEMENTARY SCHOOL, REDWOOD CITY, CALIFORNIA

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1 REPORT ON THE POTENTIAL SOURCE OF THE INSECT BITES FOUND ON STUDENTS AT CLIFFORD ELEMENTARY SCHOOL, REDWOOD CITY, CALIFORNIA PREPARED BY: DR. STEVEN L. HEYDON ENTOMOLOGICAL CONSULTING 1715 BATES DRIVE DAVIS, CALIFORNIA OCTOBER 2011

2 INTRODUCTION The problem began this fall when numerous students in three classrooms at Clifford Elementary School in Redwood City, California, began exhibiting itchy lesions attributed by doctors to insect bites. Ultimately about 20 students, one school staff member, and a family group that used the Clifford School play area were affected. Only one doctor listed the location of the bites and these were on the neck area and face. Belfor Property Restoration was contracted to pack up the rooms and treat them for insect pests. All the materials in the rooms was bagged and was going to be treated in a freeze dryer for two days before being returned to the classrooms (Figure 3). The combination of vacuum and cold temperatures should be sufficient to kill any arthropod associated with the classroom materials. However the source of the bites remained unclear and so the Belfor company contacted me to come down and sample the affected classrooms and search for insects or other arthropods of human health concern. The three classrooms involved Room K, Room 1, and Room 2, were on the northeastern corner of the school (Figure 1). They were bounded to the north by a strip of seminaturalized plantings, including a row of oak trees, and on the south side by an asphalt hallway/playground. To the east was a play area that was covered fairly deeply with chipped bark (Figure 2). The bark was not new. The basic construction of the affected classrooms was not any different from the rest of the school, but they were somewhat closer to the plantings than the other classrooms. Figure 1. The three affected classrooms at Clifford Elementary School.

3 Figure 2. Play area used by students in the affected classrooms. Figure 3. Classroom contents being packed.

4 STICKY TAPE SAMPLING One of the simplest and best techniques for sampling insects off surfaces is simply to repeatedly press strips of clear packing tape, sticky side down, onto these surfaces and then press the tape down onto sheets of white paper. In a sense you are making a giant microscope slide that can be examined under the microscope in the laboratory at a later time. Multiple such samples were taken in Room K, Room 1, Room 2, and the storage room between Room K and Room 1. In Rooms K, 1, and 2, samples were taken from areas where insects or biting mites are most likely to be found. These included surfaces around doors (especially the thresholds)(figure 4), windowsills (Figure 5), sinks (because of the availability of water), in food storage areas, and under electronic equipment. The electricity flowing through power equipment creates warmth and this increased temperature is attractive to insects. In addition, to these surfaces, the filter in the air handler for Room K was removed and sampled. A final tape sample was taken from the top of the retaining wall that runs along the north side of the play area. I was told that the homeowner there had recently taken out a number of juniper bushes, and I was looking to see if there was any evidence of biting arthropods moving into the play area from this property. A list of insects collected by the tape strips in each area follows. After that, the human health hazards presented by each kind of insect or other arthropod will be discussed. Figure 4. Door threshold in affected classroom and Clifford School.

5 Figure 5. Windowsill area in Classroom K. Classroom K: Air handler filter Tape strip samples taken from the surface of the filter was full of dust and colored cloth fibers. There was also patch of moth scales on one piece of tape that had been left behind where some moth or butterfly had been sucked into the heating unit. Moth scales are a known allergen, but repeated expose over years is needed to cause sensitization. This sensitization usually takes the form of hay fever symptoms, not itchy lesions as reported in the doctor s reports. In any case, simultaneous development of allergic reactions to moth scales by multiple students seems an extremely remote possibility. Room K: Window Sill 1. Ceratopogonidae (no-see-ums) 2. Empididae (dance fly) 3. Lepidoptera (moth) 4. Phoridae (phorid fly) 5. Encyrtidae (encyrtid wasp) 6. Cynipidae (gall wasp) 7. Pholcidae (cellar spider) 8. Sciaridae (dark-winged fungus gnat) 9. Braconidae; Aphidiinae (braconid wasp) 10. Ceraphronidae (ceraphronid wasp)

6 11. Spider exuvia 12. unknown fly 13. Staphylinidae (rove beetle) 14. unknown beetle 15. Cicadellidae (leafhopper) 16. unknown parasitic wasp Room K: Front Door 1. Argentine ant (Linepithema humile) 2. Psocoptera (booklouse) 3. Lepidoptera (moth) scales 4. Siphonaptera (flea) 5. Staphylinidae (rove beetle) 6. Dermestidae (carpet beetle) larva 7. Cecidomyiidae (gall fly) 8. Spider evuvia 9. Lepidoptera (moth) pupa Room K: Back Door 1. Dermestidae larva (carpet beetle) 2. Psocptera (booklouse) 3. probably a parasitic wasp head Room K: Spider Web on Wall 1. Thysanoptera (thrips) 2. unknown insect legs Room K: Under Power Strip 1. Dermestidae (carpet beetle) larva 2. wing fragment 3. spider web debris Room K: Pantry Area 1. no insect or arachnid remains visible Room 1: Window Sill 1. Thysanoptera (thrips: 2 species) 2. Psocoptera (booklouse) 3. Staphylinidae (rove beetle) 4. Sciaridae (dark winged fungus gnats) 5. Cecidomyiidae (gall midges)

7 6. Chironomidae (midge) 7. Mymaridae (fairy wasp: 2 species) Room 1: Front Door 1. unknown insect skin 2. Dermaptera (earwig) nymph and ant head in spider webbing 3. spider exuvia 4. partial ant bodies, probably of Argentine ants (Linepithema humile) 5. unknown insect leg 6. arachnid exuvia 7. fly leg 8. insect abdomen, probably termite or cockroach nymph Room 1: Back Door arachnid body, possibly a mite but the condition was very poor, probably dead The Storage area between Room K and Room 1 was extensively sampled due to the great number of insect and other arthropod traces visible there (Figure 6). Several areas were checked in the storage room. One was the wall with the windows in it and which had storage cabinets stacked up in front of it. These storage cabinets made cleaning this wall difficult. In addition to that, a gap under the door in that wall provided ready access for entry by outside arthropods. Hence a large population of spiders had built up as evidenced by the large amount of webbing found there (Figures 7 & 8). Samples of the webbing and other arthropod debris scattered around were collected to see if known species of venomous spiders, any mites, or other insects were present there. The webbing was very soft and broke easily, so black widow spiders were probably not present. No remains of their bodies were seen in the web samples, and no egg sacks were seen so black widows were either absent or present in only small numbers. Most of the spider remains were of cellar spiders, Pholcus phalangioides and Holocnemus pluchei. These spiders may be abundant in human dwellings, but are not known to be a biting hazard despite folk information otherwise. Other small spider remains were present, but none of the species that are know to cause venomous bites in humans were found. Other arthropods collected there included: Argentine ant (Linepithema humile), fungus gnats (family Mycetophilidae), millipedes, springtails (Collembola), booklice (Order Psocoptera), isopods, dragonfly wing bits, carpet beetle larval skins, parts of another unidentified beetle, and the remains of a housefly (Musca domestica). The only thing in this sample that is of concern to human health is the carpet beetle skins, which are known to be an allergen ( However since long-term exposure is needed before a reaction occurs, it is unlikely that the carpet beetle skins are the source of the bite reactions in the students. In any case, these beetles can be found in most homes and so the exposure at the school would be in addition to the exposure they would be getting at home. It is not possible for a simultaneous outbreak of allergic reaction. No mites were found in the samples from this area.

8 Figure 6. Storage room between Room K and Room 1.

9 Figure 7. Spider webs in Storage Room

10 Figure 8. Debris behind storage cabinets in Storage Room.

11 The second area checked in the storage room was the surfaces of some bookshelves that exhibited splotches of black mold (Figure 9). Frass was noted among the mold spores, but the source of this frass could not be determined. The frass particles were very small so a very small insect or other arthropod was responsible. Insect parts that were found on these surfaces were similar to those found in the spider webs examined above including ant wings, carpet beetle skins, bits of spider cuticle, booklice, and bits of dragonfly wing. None of these except possibly the carpet beetle skins are of any medical concern. Figure 9. Storage cabinet with mold. Storage Room: Interior Shelves 1. Argentine ants (Linepithema humile) 2. Pholcidae (cellar spider) exuvia 3. unknown insect wings 4. Psocoptera (booklouse) 5. Thysanoptera (thrips) 6. Acalypterate Diptera wing 7. Diapriidae (diapriid wasp) 8. arthropod fragments Room 2: Window Sill 1. Sciaridae (dark-winged fungus gnat) 2. Culicidae (mosquito) wing fragment 3. Mymaridae (fairy wasp) 4. Psocoptera (booklouse)

12 5. Cecidomyiidae (gall midge) 6. Mycetophilidae (fungus gnat) 7. Acalypterate Diptera, possibly Chloropidae (frit fly) Room 2: Front Door 1. spider web debris including spider exuvia, ant bodies, and Sciaridae (dark-winged fungus gnat), winged Psocptera (booklouse), Dermestidae larvae (carpet beetle), and unknown insect head. 2. Psocoptera (booklouse) Room 2: Back Door 1. Diptera (fly) antennae Room 2: Air Handler vent 1. no evidence of any arthropods present Retaining wall along north side of play area 1. Psocoptera (booklouse) wings KNOWN HEALTH AFFECTS OF ARTHROPODS RECOVERED. Isopods and Millipedes Isopods (sow bugs or roly-polies) and Millipedes are scavengers with relatively weak mouthparts incapable of biting humans. Some millipedes can excrete noxious fluids when handled, but none of the North American species can produce symptoms like those seen on the Clifford students. Spiders Spiders are venomous arthropods. They use their poison to subdue their prey. The number of species that are harmful to humans is relatively small because most do not live where humans are, they are shy and not aggressive, they have weak venom, or they are too small for their fangs to penetrate human skin. The tape sampling only picked up the shed skins (exuvia) of spiders so precise identifications were usually not possible. The spiders that could be identified were cellar spiders, probably either Pholcus phalangiones or Holocnemus pluchei, neither of which are known to be harmful to humans. None of the exuviae appeared to belong to black widow spiders or other species known to be harmful to humans.

13 Mites Mites are one of the most likely culprits in most cases of human bites of unknown origin. Out of all the thousand of species of mite, there are a handful that can cause trouble for humans including chiggers, the hay itch mite, the Oriental rat mite, and a few bird mites. One possible mite was recovered, but its condition was too poor for a definitive identification. My general impression was that it did not look like the biting mites I have seen recovered in other locations. The mite recovered was relatively robust in build more resembling the soil mites. In my experience, mites are usually picked up in structures after the extermination or emigration of known hosts including rats and nesting birds. Dermaptera The earwigs are predators on other insects or general scavengers. They can pinch a bit with the forceps on the end of their abdomen, but they are not medically important. Thysanoptera Thrips are a diverse group of insects. Some are plant feeders and some are predators on insect eggs or other small and weak insects. Some species are known to bite humans. If you sit in the grass in the summer, you may occasionally feel a sharp itching pain and if you look quickly and carefully, you will see a minute slender orange or brown insect crawling away. There is increasing evidence that the bites of thrips can cause a reaction in humans resulting in a rashlike skin condition (C. C. Childers et al. 2005, Florida Entomologist 88: ). Thrips are weak fliers, but can be carried by wind or encountered when moving through airspaces containing these insects. Hemiptera The leafhoppers, the Cicadellidae, are plant feeders on plants. They cannot bite humans and are not any threat to human health. Psocoptera The Psocoptera, or booklice, are general scavengers that are commonly found in domestic situations when the humidity if relatively high. Homes in the Central Valley of California seldom have trouble with them, but they may be common in buildings along the coast. They are not harmful to human health, but they may destroy household furnishings or food. All specimens found in the rooms are probably the common booklouse, Liposcelis corrodens. Siphonaptera Fleas are well-known as blood feeders on vertebrates. The most common fleas in domestic situations are the cat and dog fleas. Fleas are unlikely to infest a classroom since the larval stages need to feed from blood and other debris that comes from the host.

14 Nesting places are where the larval stages of fleas are found and the adults can be found in areas frequented by the mammals that carry them and then jump off or be groomed off the animal. I suspect this flea came off a feral cat, but transport to school on a human is also possible. Diptera A number of Diptera were found in the tape samples including: Culicidae, the mosquitoes, are among the most deadly of all insects since a number of species can transmit diseases in human populations. These diseases are well controlled in North American, but some people have strong allergic reactions to the chemicals injected at the bite by these insects. Reddened swelling may occur that will go away without incident in a few days. However if these bites are scratched, serious secondary infections may occur. Such scratching may occur at night during sleep. The no-see-ums, or Ceratopogonidae are minute blood-feeding flies. Like mosquitoes, the females need a blood meal to mature eggs. These flies are small enough to get through ordinary window screens and into houses. When their bite is occurring, it can be quite painful and the flies can be seen as small slender black dots on the skin. They are a particular plague at my house in Davis at certain times of the year. The bites of ceratopogonids generally take the form of quarter inch round red discs that may itch intensely. These flat bites contrast with the swelling associated with the bites of mosquitoes. However, like mosquitoes, if these bites are scratched, dangerous secondary infections may result. The Sciaridae, Phoridae, and Mycetophilidae are general scavengers and feed on fungus or other microorganisms associated with decay. The adults have rudimentary mouthparts and are of no medical threat to humans. The Cecidomyiidae, or gall midges are small flies that lay their eggs inside plants. A characteristic swelling is normally induced, inside of which the fly maggot feeds and grows. The adults have rudimentary mouthparts and are of no medical threat to humans. The Empididae, or dance flies, are small to minute predatory flies that are not known to bite humans. The Acalypterate Diptera is a group of small flies, one family of which is the Chloropidae. Most all the acalypterates are harmless to humans, but one group of chloropids, the eye gnats, feed around the edges of eyes and can be quite annoying. They can also transmit pink eye between humans, however none can cause bites and the rashes seen in the children at the school. House flies (Muscidae) are scavengers and the adults have mouthparts incapable of biting humans. Their major health threat is as a carrier of disease organisms on their feet from one place to another.

15 Coleoptera The carpet beetles (Dermestidae) are scavengers and feed on dead organic matter of all kinds including hair, wool, stored products, and museum and taxidermied specimens. They are found in almost every home feeding on the dead insects and human hair and skin cells we are continually shedding. They cannot bite, but humans can build up an allergic reaction to their shed larval skins with repeated exposure over time. Rove beetles (Staphylinidae) are general insect predators. They are not known to bite humans. However sometimes when some of the small species are out flying in numbers, they can cause extreme irritation if they get into the eyes while biking (personal experience in Davis). Hymenoptera Fairly wasps (Mymaridae) are the smallest of all the insects. The female wasp lays her egg in the egg of another insect. All the food the fairly wasp larva requires to grow to adulthood is supplied by that one host egg. These wasps are so small (< 1mm in most cases) that they are harmless to humans. Other families of parasitic wasps found in the classrooms included Encyrtidae, Ceraphronidae, Diapriidae, and Braconidae (Aphidiinae). These wasps are very small and do not have stingers. These are quite different families taxonomically, but for the purposes of this report, they have similar biologies and can cause no physical harm to humans. The Cynipidae are commonly known as the gall wasps. They lay their eggs in oaks and the growing larvae forms a characteristic plant growth called a gall. The wasp larva feeds on the plant material as it grows and matures. These wasps are very small, 2-4 mm in length, and cannot sting or harm humans in any way. The Argentine ant is an introduced species that has become naturalized throughout California. They are common inhabitants of human structures. They can occasionally bite, but I have never heard of any long-term problems or lesions resulting from these bites. GLUE BOARD SAMPLING Glue boards were set out in all of the rooms and in the play area. About half of the glue boards in the classrooms were examined. Very few insects were seen stuck in the glue boards in the classrooms and most of them were Psocoptera (booklice). Glue boards were also set out in the play area (Figure 10). These collected numerous insects characteristic of urban situations. Stinging insects like yellow jackets were found, but the injuries caused by stinging insects are much different than what is reported by the children.

16 Figure 10. Glue boards from playground. OAK TREE SWEEP SAMPLES Along the north edge of the property, and adjacent to the playground used by the students in the affected classrooms, there was a row of live oaks (Figure 11). In the Midwestern United States, there is a mite associated with oaks that has been known to bite humans especially in the fall. This mite is called the oak leaf gall mite or simply the itch mite, Pyemotes ferfsi ( pcitchmites.htm). They normally feed on the maggots of small flies (Cecidomyiidae) that live in swellings along the edges of oak leaves. At certain times, especially the fall, the maggots leave the galls and the food supply of the mites disappears. The mites then drop from the trees and bite whatever they can land on this includes people. The bites are on the upper part of the body in contrast with the bite of chiggers, which are on the lower parts of the body. Chigger mites also tend to just bite once and feed there, while the itch mites bite many times in clusters since they are trying to feed in a host other than their natural one and probably encounter feeding difficulties from mammalian blood clotting factors etc. A sample was taken by sweeping the oak trees with a fine-mesh net to sample for any mites living there. This net would collect any mites that were present. The sweep sample was examined back in the laboratory and no mites were found. Furthermore, the leaves of the oak were not galled, ruling out the presence of a fly host, and so the itch mite can be eliminated was a source of the bites seen on the children.

17 Figure 11. Oak trees and retaining wall along north side of play area. However this sample did contain other insects that are known to bite humans. Green lacewings, family Chrysopidae, have larvae that have long, curved, tusk-like mandibles that are designed to pierce the bodies of their insect prey, inject digestive juices and then suck the digested insect guts back out. These larvae can bite humans painfully ( I have been bitten by them numerous times while out collecting insects, but never suffered any kind of subsequent reaction to the bites like that exhibited by the students. The three individuals recovered were all very early instars and I do not think these very small insects would have the jaw strength to penetrate human skin. So lacewing larvae are a possibility, but remote, source of the bites suffered by the children. Another insect found in the sweeping samples were thrips. Thrips are a small insect with sucking-rasping mouthparts. They are common in the summer in grassy areas and certain species bite humans, mistaking them for their natural insect or plant foods ( Once again, I have often been bitten by them and never had any skin reaction to the bites, but the scientific literature records other people getting itchy rashes from thrips bites (C. C. Childers et al. 2005, Florida Entomologist 88: ). Little data is available on which species of thrips bite and which don t.

18 NESTS FOUND IN STORAGE AREA BETWEEN ROOM K AND ROOM 1. Three bird nests were found in a drawer in the storage room (Figure 12). Some of the most problematic biting mites are those associated with nesting birds. The mites feed on the blood of the baby birds and then when the chicks fledge and leave the nest, the mites are desperate for another source of food. If the nest is on a human dwelling or other structure, the mites spread out and will bite humans and other animals. They cannot reproduce indefinitely on humans, but it may take quite a while for the infestation to die out. The nests were examined and mites were found. An exact identification of the mites was not made, but they do not have the overall form of the biting mites. They exhibited none of the characteristic signs of having blood fed. The teacher to whom the nests belonged had not used the nests in their classroom since last year. These nests do not seem to be the source of the bites seen on the children. Figure 12. Bird nests in storage room between Classroom K and Classroom 1.

19 SUMMARY AND RECOMMENDATIONS The exact cause of the bites exhibited by the children is uncertain. Four insects were recovered in my surveys that could have bitten the students mosquitoes, no-see-ums, fleas, and thrips. I do not think any of these insects are or could infest the school classrooms since they all require breeding conditions that are not found in classrooms such as those found at Clifford Elementary. Mosquitoes breed in standing water and there was no evidence of that on the grounds that I could see. There were no water features in the landscaping that I remember. The no-seeums also reproduce in moist habitats with organic matter. It is possible that they could be reproducing in the moist layers of the bark chips in the playground, but as a general rule, no-see-ums prefer alkaline soil conditions to reproduce. The no-see-ums are far more likely to be reproducing somewhere along the salt marshes of the coast and then dispersing throughout the city. Neither the mosquitoes nor the no-see-ums are likely to be restricted geographically to the school grounds and therefore under your control. According to the doctor s reports, one of the students was showing symptoms of the bites before school started indicating to me that the insect doing the biting was probably generally distributed in the city. As mentioned earlier, fleas reproduce in the nests or other habitual resting places of vertebrates where the immature fleas can find the blood and other organic material they need to eat in the fecal matter of the adults. The school grounds seem clean and well cared for with no animals resident on the grounds, so I do not feel a flea infestation is the source of the bites. The flea found in the survey may have been carried to school from pets at home, or it may be from feral cats living in the unmaintained grounds around the school. I think feral cats or even roaming neighborhood cats are the likely source of the flea found. Another bit of evidence against fleas being the culprit are the location of the bites. In my experience, fleabites are more likely to be on the lower extremities where the fleas can reach by jumping onto a passing person. The one student whose doctor listed the location of the bites said they were on the head and neck area. This leaves the thrips, If I had to guess as to the source of the itchy lesions, and assuming they were actually caused by insects, I would say thrips are the most likely culprit. Thrips are common insects in California and were found in many of the samples from the school. I noticed that I got many bites this fall from thrips here in Davis in the weeks just before this investigation. Thrips bites are not known to be especially prone to causing itchy lesions in humans, but I suspect their importance as biting insects is underestimated. Numerous thrips were recovered from the sweep sample of the oak trees near the affected classrooms. The affected classrooms were those nearest the oak trees and used a playground right under these trees. The bites were on the upper areas and exposed areas of the body, which is where thrips tend to bite. The main problem with thrips is control. They are native insects and are probably found in all the oak trees in and around Redwood City. Chemical control could be applied to the

20 oaks growing on the school grounds in the late summer and early fall to keep their numbers down while school was in session. Alternatively, the oaks in the vicinity of the playground and those first three classrooms could be taken out and other trees could be planted. The oaks are very nice because they are native trees, but because they are from here, there are many many insects adapted to living in oaks and using them either as food or as supporting the insect that they in turn eat. The scales and the parasitic wasps, the green lacewings, the gall wasps, and the thrips all call the oak trees home. The yellow jackets and Argentine ants probably rely on the honeydew produced by the scale insects and other phloem feeding insects for part of their food. An arborist could probably help with selecting tree species that would support fewer insect species. Another alternative would be to monitor the usage of the windows in those classrooms. The quantity and diversity of the insects and other arthropods recovered from Room K indicate to me that the windows to that classroom may be open most of the time. That is nice for temperature regulation and fresh air circulation, but it also lets in insects. Perhaps not opening the windows on the north side of this classroom might help. A final suggestion is to remind teachers that bird nests are hosts to huge populations of mites that could potentially be a source of biting arthropods. They are nice teaching materials, but they should be treated before use by storing them for a couple weeks with mothballs in Ziplock bags.