Spiders and Insects of Alaska

Transcription

1 Spiders and Insects of Alaska Spiders There are no spiders in Alaska that pose a toxic threat to humans. Every spider is venomous and pose a threat to their prey! Every year the Section of Epidemiology hears about a small (generally five or fewer) number of Alaska residents who believe they have been bitten by spiders. Nearly all are from Anchorage, the Kenai Peninsula, or the Mat-Su Valley. Most bites have been relatively minor and resolved without any specific treatment. A few of the reports have been of more serious problems such as necrotic lesions requiring skin grafting. The purpose of this Bulletin is to summarize what is known about spiders in Alaska and spider bites. Spiders are not inherently aggressive but will bite when threatened, for example, if trapped between clothing and a person's skin. Spider bites are rarely witnessed. Most often a skin lesion is discovered with an appearance that is compatible with a spider bite (as well as other arthropod bites or minor skin irritations). While a bite from any spider might cause a localized inflammatory reaction with some tissue damage, for the most part, the resulting lesion is not extensive. Often lesions diagnosed as spider bites result from another cause and conversely, lesions actually caused by spider bites could be misclassified. Therefore, very little accurate data exist on the incidence or outcomes of spider bites. In most cases, confirming the diagnosis and identifying the biting spider are not necessary, because the majority of spider bites require only symptomatic treatment. Nearly all spiders possess venom of some sort, and therefore could be considered "venomous." In this Bulletin, "venomous" spiders refer to those possessing venom capable of causing medical problems for humans. Naturally occurring spiders in Alaska Multiple families of spiders naturally occur in Alaska. The most common biting spiders in Southeastern Alaska are from the genus Callobius. Bites from these spiders cause immediate pain and swelling which generally subsides within a few hours. Seriously venomous spiders do not occur in Alaska: these include those from the Loxosceles (recluse) and Latrodectus (widow) genera which can cause severe local as well as systemic effects. Version 1.0 1

2 The Hobo Spider The only major venomous spider possibly found in Alaska is the hobo spider, Tegenaria agrestis, which was introduced from Europe to the Pacific Northwest in the 1930s. While the range of the hobo spider could extend into the Alaska panhandle, the Hobo Spider has never been positively identified anywhere in Alaska. Sexually mature hobo spiders are common mid-summer through fall, at which time males wander in search of females who usually remain near their webs. Hobo spiders are rarely found above ground or basement level. Males are more venomous than females. Although both sexes will bite, males are more often implicated in bites as they are more active and therefore more likely to come into contact with humans. Hobo spider bites can cause serious tissue necrosis and, in rare instances, severe and even fatal sequelae. Venom is injected in only about 50% of bites. Bites from these spiders are usually painless and initially form an expanding erythematous ring that may reach up to 15 cm in diameter. Blisters form around the lesion within hours, and subsequently rupture producing a serous exudate that crusts around the crater wound. Underlying necrosis and sloughing of affected skin usually causes significant scarring with most wounds healing by 45 days. Bites can induce systemic symptoms, ranging from a persistent headache (the most common) to severe blood dyscrasias. Tegenaria agrestis, the Hobo Spider, actual size approximately 2-4 cm. Numerous other species of spider share this appearance. No consensus treatment protocols exist. Generally, treatment of Hobo spider bites involves local wound care, monitoring for systemic effects, and review of tetanus vaccination status. Antibiotics may be indicated should secondary infection arise. Serial photographs of extensive lesions should be taken to record changes over time. Bites inducing systemic effects might necessitate the use of systemic corticosteroids as well as transfusions of blood products. Version 1.0 2

3 Preventive measures Measures to reduce exposure to spiders are the most efficient and effective methods of avoiding spider bites. Personal protection includes using gloves or other protective clothing that covers skin while working in crawl spaces and similar locations, and when retrieving firewood or objects stored in potentially infested areas. Prior to use, shaking out clothes, shoes, and other items that have been stored is also prudent. Screens on basement and ground-floor windows and insulation strips under doors may reduce the risk for spider infestation. To prevent spiders from gaining access to beds, bedspreads should be kept at least 4 inches above the floor. Further information about spider-proofing homes is available from the Alaska Co-operative Extension at Summary Necrotic lesions with a history compatible with that of a spider bite should prompt health care providers to: Contact Poison Control at (in Anchorage or outside the city); or Dr. Michael Callahan, Envenomation Consult Service, mica@rescuemedicine.com for assistance in treating spider bites; If the suspected spider is available (place in alcohol if possible), contact Alaska Cooperative Extension at ; or Rod Crawford at the Burke Museum in Seattle, WA at or tiso@u.washington.edu for assistance in identifying the spider. Accurate identification of spiders is difficult and requires microscopic examination of various anatomic parts by an expert. Color or body markings alone cannot be used to definitively identify the species of a spider. 1 1 Bulletin No. 17 November 1, 2000 Spider Bites in Alaska Version 1.0 3

4 Insects Alaska is notable for its insect exceptions. For example there are no fleas in Alaska. No cockroaches or ticks either. But it is also notable for its extreme populations of mosquitoes. Click here for an insight into this challenge. Mosquitos Forget about bears - what really strikes fear into the hearts of Alaskan backpacking trekkers are mosquitoes. The belief that Alaskan mosquitoes are large enough to carry off small children is a part of the dis-information campaign perpetuated by Alaskans to discourage others from moving here. Alaskan mosquitoes are no larger than elsewhere, but what they lack in size they make up for in sheer numbers. June is prime bug season and at lower elevations they can get pretty horrific in places. In the mountains however they usually aren't as bad. You might want to carry a head-net if you're planning a trip in June, as well as some bug juice. First time Alaska backpacking adventurers often overreact to bugs, hosing down with DEET at the first sight of a few mosquitoes, while the locals don't even seem to notice. Sometime around mid August the bugs begin to die off and cease to be a problem even at lower elevations. There are insect repellents that use natural ingredients such as Citronella which vary in effectiveness though their efficacy is generally short lived at best. DEET remains the most effective and longest lasting repellent. Wearing lighter coloured clothing may also help to minimize bug attraction. Clothing with a very tight weave will keep bugs from biting. Alaska Mosquito Tips If you do find yourself in a heavy congregation (mosquitoes seem to be most active at dawn and twilight), there are easy steps you can take to block out the nuisance: o Try to expose as little skin as possible. Wear shoes, long sleeves, and long pants with the cuffs tucked into socks. o Tight-weave cotton shirts and pants work better than more porous synthetics o Wear khaki or neutral colors. mosquitoes are attracted to dark colors, especially blue o Don t use scented soaps, lotions, or shampoos o If you re taking a multi-day backpacking or float trip, bring a headnet for backup Version 1.0 4

5 o Use repellent. Other Insects The list below reference beneficial spiders and insects. Think of it as a handy reference guide. Harvestman/Daddy Long Legs Slightly different looking spider to the Daddy Long Legs we see in Australia. No web. Several species in Alaska. Technically not a spider (!) Ground or Wolf Spider Seems a little larger than the Wolf Spiders we know around Sydney but similar colouring. No web. Lives in tunnels. Fast runner. Excellent eyesight. Nocturnal hunter so you will see its eyes reflecting like bright LEDs on the track. (Not that we are likely to be out in the dark in Alaska! Crab Spiders Similar to the crab spiders we see around Sydney. Very cool look like crabs given their first and second legs are much longer than the third and fourth pair. Ambush their prey (no web). They will be found in flowers. Can slowly change their colour to match the flower they are sitting in. Version 1.0 5

6 Orb Spider Similar to the orb weavers we see around Sydney. Renown for their size. Massive, well engineered webs. Females spin webs, and are much larger than the male. Numerous variation on colour and markings. Damsel Bugs Lacewings As for Australia. Green and Brown versions. Ground Beetles Similar to Australian versions. Matt and metallic colours, with ridged wing shells. Can t fly. Version 1.0 6

7 Lady Beetles Flower Flies As for those we see in Australia, though potentially with much more variety of colour. Also very similar to what we have around Sydney. You know what they look like. Robber Flies Large and strong. Generally ambush other insects while in flight. Version 1.0 7

8 YellowJackets Parasitoid Wasps You might know this as the European Wasp. Capable of multiple stings. Territorial in the same way hornets can be territorial. Can get aggressive. Loves sugar and honey notorious for entering opened soda cans and being ingested by the unwary. Lightly built but fast and agile. Lays its eggs in other insects nasty. Parasitoid Flies Looks like most other flies actually (!) Version 1.0 8