by Whitney Cranshaw
Colorado State University Extension Specialist (4/09)
County offices not infrequently get client questions and referrals from public health agencies, medical facilities, and pest control companies regarding arthropods suspected to be involved in stinging and biting humans. Because of the human health implications, such queries must be handled very carefully. Our role is to provide accurate identification of the arthropods that might be involved, while at the same time avoiding anything that might be construed as the practice of medicine (e.g., examination of bites or other symptoms).
There are several resources that may be useful for handling such samples, which are reviewed below. These should allow county offices to handle most of these types of samples. However, whenever positive identification is not possible the sample should be sent to campus; misidentifications can have serious medical and financial implications.
One unacceptable sample type is those involving “bites” of the person (i.e., the client displays a bite and asks counsel). We can only identify arthropod samples that the client provides, and can never diagnose a cause of a bite. The latter are clearly a medical issue and the client must be referred to a physician.
Bed Bugs and Related Species. The issue of bed bugs, unfortunately, will become much more important in the next few years as this insect spreads within the state and in people=s consciousness. In addition, Colorado has some related species of insects, notably bat bugs and swallow bugs, that move from wild animal hosts and may bite people. A guide to identification of these insects and management is covered in the recent revision of the fact sheet Bed Bugs, Bat Bugs and Relatives.
A key to these bugs is in the fact sheet but some of the identifying features are difficult. If positive identification is not possible (e..g., bed bug or bat bug?) then it should be sent to campus for positive identification.
Fleas. Flea issues within homes in Colorado are uncommon due largely to the dry climate. Occasionally they do occur, most often from transfer of fleas originating from animal dens (e.g., fox, skunk) or squirrel nests. In addition, the flea-vectored disease plague is endemic in certain rodent populations within the state and occasionally involves human fatalities. The general situation on this subject is summarized in the fact sheet Fleas and Plague.
This sheet should be sufficient to identify a flea. However, if you want to get a positive identification on the species of flea, this will probably have to be sent to campus.
Issues involving plague are the clear responsibility of state, county and local public health agencies. Extension should only be involved in plague issues if support is requested by these organizations.
Ticks. Several species of ticks do occur outdoors in Colorado; only one of these can complete its life cycle indoors on dogs, the brown dog tick. Most ticks that are encountered are the Rocky Mountain wood tick, Dermacentor andersonii, which is picked up by hikers and dogs during spring and early summer. If positive identification of ticks is needed they should be sent to campus. However, unusual species may need to be sent outstate for positive identification.
Within Colorado, ticks are also involved in transmission of several diseases, notably Colorado tick fever. Fortunately, the most important tick-borne disease in the US, Lyme disease, is not an issue and there have never been human cases of Lyme disease that originated within the state. However, Extension offices should never be asked to diagnose disease symptoms, only to assist in tick identification. Some assistance to the client may be found in the fact sheet Ticks and Tick-borne Diseases.
Lice. Head lice are a widespread and not uncommon problem in Colorado, mostly among school children. School nurses and many public health agencies are well acquainted with this problem and therefore no Extension fact sheets have been developed on this issue. If additional information is needed the Harvard School of Public Health web site providing head lice information is recommended at: (www.hsph.harvard.edu/headlice.html ).
Occasionally other sucking lice, such as the crab louse (“crabs”) are brought in. Other lice from livestock and birds may be brought to county offices. Although the crab louse is quite easily identified it is probably best that all suspected lice are sent to campus for positive identification.
Mosquitoes. Mosquito concerns in Colorado have intensified greatly since the establishment of West Nile virus in the region. Also, the Colorado Department of Health and the Environment maintains a “Fight the Bite Colorado” website, www.fightthebitecolorado.com/, with additional information and links.
Issues of mosquito-borne diseases, such as West Nile and the other equine enchephalitis viruses that occasionally occur in the state , are handled by state and local public health agencies. Extension involvement with area-wide mosquito management and West Nile should only be done in close coordination with these lead organizations.
Spiders. Spiders found in and around homes attract tremendous attention and often concern. Some medically important species do occur in the state, notably the western widow, and most issues involve clients wanting to know that the spider they have is not dangerous. Almost invariably the spiders are not dangerous species and the common spiders found within the home are summarized in the fact sheet Spiders in the Home.
The western widow spider – the “black widow” of the west – is the primary species found in Colorado that has human health implications. This is covered in the fact sheet Western Widow Spider.
High concerns about brown recluse spiders also occur. This spider is >extremely< rare in Colorado and much of the concerns stem from spider misidentifications (typically with funnel weavers) and from misdiagnosis of “bites”(mostly with methicillin resistant Staphylococcus aureus/MRSA infection). This subject is handled in the fact sheet Brown Recluse Spiders in Colorado: Recognition and Spiders of Similar Appearance.
A special spider issue is the “hobo spider” and its purported danger to humans. This originated from an unfortunate study that suggested this spider could cause slow healing wounds similar to those known to be sometimes produced following a brown recluse bite. This report received extremely wide distribution in popular press and the internet. However, subsequent research has demonstrated that this original report was erroneous and based on unsupportable anecdotal evidence. The hobo spider is now recognized as >not< being a dangerous species. It is a harmless funnel weaver spider and is now found in many areas of the state.
Spider samples sent to campus can easily be identified to the family level. Common species of household spiders and the few that have medical importance can usually be identified to the species level. However, species level identifications of spiders are very difficult and generally feasible only with samples of adult males in good condition. Fortunately most client queries involve common species and/or whether the spider in question is a dangerous species.
Bees and Wasps. Most stings are caused by yellowjacket wasps followed by other wasps and a few bees. This subject is covered generally in the fact sheet Nuisance Wasps and Bees. A separate fact sheet on the European paper wasps is available at: http://extension.colostate.edu/topic-areas/insects/european-paper-wasp-5-611/
Mystery Bites/Invisible Itches. There are few more difficult and frustrating client queries than those where there is a purported “bite” or some generalized itch that the client insists is caused by an insect or spider. These situations may actually involve an arthropod; often they have other causes. In extreme cases delusionary parasitosis may become an issue, which can become a situation that produces debilitating effects on the life of the client.
Some guidance for handling these situations is in the paper Mystery Bites and Invisible Itches – Arthropod and Non-Arthropod Causes in Colorado. This lists what kinds of arthropods can be involved in bites/itches and under what conditions they occur. Diagnosis of some of these are covered in fact sheets; others (e.g., scabies diagnosis) can only be done by a physician.
It should be reemphasized that central to any such client query is the rule that no diagnosis can ever be done based on the “bite” alone. However, we are capable of identifying material that the client submits for the presence of arthropods. If you need help with such a problem then contact one of the Extension entomology people on campus and we will take over working with the client.
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The above resources should provide assistance/guidelines that could help you with 95%+ of the client queries involving arthropods of medical importance in Colorado. A few gaps still exist (e.g., scorpions, masked hunter) but these will be covered in future publications.
When submitting an arthropod sample involving a potential medical issue it is best to contact a person before hand (contact information below). Although samples sent to the CSU entomology group sometimes to get slowed down, particularly as research programs divert much attention and travel peaks during the growing season, arthropod samples with medical implications always get highest priority for attention.
Campus Entomology Staff with Partial Extension Appointments
Address: Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO 80523
Whitney Cranshaw
email: Whitney.Cranshaw@ColoState.EDU
Phone (office): (970) 491-6781 (Note! If I do not answer the phone never leave a phone message at this number as there are long periods of time when it does not get checked! Email the message and/or leave a phone message at the lab number.)
Phone (lab – best # during field season): (970) 491-7554
Frank Peairs
email: Frank.Peairs@ColoState.EDU
Phone (office): (970) 491-5945
Matt Camper
email: Matt.Camper@ColoState.EDU
Phone (office): (970) 491-0713
Phone (lab): (970) 491-7554
