Utah Pests News Fall 2008

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UPPDL Common Submissions: Arachnids, Wasps, and Bees

  Fig. 1. Hobo spider 
The end of August is a busy time at the UPPDL, mostly occupied by identifying hobo and non-hobo spiders.  Hobo spiders (Fig. 1) will be wandering into homes from now until mid to late October.  For more information on hobo spider biology and control options, please read our fact sheet. For information concerning the identification of hobos, see our pictorial identification key.

Hobo spiders aren’t the only arachnid visitors you can expect to see this fall.  Another spider common to Utah homes, the yellow sac spider (Miturgidae: Cheiracanthium inclusum), will also be moving inside as temperatures drop.  While hobo spiders move into homes searching for mates, yellow sac spiders move inside to find food.  As autumn progresses, cold temperatures will decrease the sac spider’s food supply. In a warm house a spider can find insects all winter long, so get out those vacuums and start cleaning up potential spider food.  Without food, spiders will leave your house and search elsewhere.

Yellow sac spiders (Fig. 2) are medium-sized spiders (about the size of a nickel including the legs) and are yellow to yellow-green in appearance.  They are most often seen in homes on walls, ceilings, and in the corners of rooms.  As their name suggests, they spin day-time retreats (usually in ceiling corners) that look like little white cocoons, or sacs.  At night they leave the sac and begin searching for food.  Because of their nocturnal habits, most bites are likely to occur while you are sleeping.  A good way to reduce your chance of receiving a bite is to remove your bed skirt and move the bed 8 inches away from the wall.

  Fig. 2.  Yellow sac spider
While hobo spiders receive much recognition over their supposed necrotic bite, the bite of the yellow sac spider is also potentially necrotic, but to a lesser degree.  It is believed that the majority of spider bites Utahns receive are actually from yellow sac spiders, not hobos.  Most bite victims will notice redness and sometimes pain at the bite.  Usually, the bite will just go away at this stage, but for those who are more susceptible to the spider’s venom, a blister may develop followed by a small necrotic spot.  To minimize potential health complications, infected bites should be treated by a medical doctor.  If it is possible, you should collect the spider that bit you and submit it to the UPPDL for identification.

Fig. 3. Adult male camel spider  
Recently in the news there has been a lot of hype concerning camel spiders that is not true.  I would like to dispel the myths surrounding camel spiders (Fig. 3), which are also known as sandspiders, sunspiders, sunscorpions, windscorpions, and solifugids.  They are arachnids like true scorpions, ticks, mites, and spiders, but they are in a different order than spiders—Solifugae (and collectively referred to as solifugids).  One of the major ways they differ from spiders is that they do not have venom glands.  Solifugids are non-venomous!  Even if they had venom glands, they do not have fangs or a stinger with which to deliver venom.  W ithin the order Solifugae, there are two families containing about 120 species that occur in the United States: the Ammotrechidae and the Eremobatidae.  To view pictures of these families click here.  Worldwide, there are 12 families containing about 1095 described species.

  Fig. 4.  “False” photograph of camel spider. Because of the angle this photo was taken, the arachnids appear to be 5 to 7 times their actual size of about 2.5 inches.
Most of us have seen the picture of the soldier holding two (seemingly) huge camel spiders with a pair of pliers (Fig. 4).   That picture was taken to make those arachnids look huge.  Incidentally, the largest Middle East solpugids (members of Solpugidae, a family within Solifugae) are about 2.5 inches in length, which is how big the camel spiders in that picture actually are!  The largest solifugids occur in Africa, where they can reach up to 6 inches (including the legs).

Solifugids are common to arid regions of the southwest, including Utah.  They are nocturnal and spend their days hiding beneath objects, or in burrows.  They are predaceous, feeding on other insects and in some cases even small lizards!  They look fierce because of their large chelicerae (mouthparts), which stick out far from their head.  These are used for subduing and mashing/grinding insect prey.  In the U.S., solifugids reach lengths of 1 to 1.5 inches; pretty small compared to the size of the solpugid in the “false” picture above (Fig 4).  Solifugids should be considered beneficial predators.  They are native to Utah and were here long before we were.  Solifugids are considered beneficial hunters, and no chemical control is recommended.  Next time you are camping in southern Utah, go out at night and search the ground below with a flashlight. You are likely to see many solifugids running around!  For more information on solifugids and spiders (and their myths), click here for the Burke Museum (WA) Web site.

  Fig. 5.  Adult female sand wasp
Another frequent submission to the UPPDL this summer, in addition to hundreds occurring in my back yard (over which I am ecstatic), were the solitary, ground-nesting bees and wasps.  In particular we received numerous calls concerning ground-nesting Bembix wasps, and Diadasia bees.

Wasps in the genus Bembix are also known as sand wasps (Fig. 5).  As their name suggests they prefer to colonize sandy soils.  These are non-aggressive wasps that live a solitary life (one wasp per hole), but usually colonize an area en-masse.  These groups of solitary wasps are called aggregations, and can be intimidating at first.  Sand wasps rarely sting, if at all.  Coincidentally, males spend the night outside the nest, keeping guard.  While the males are territorial, they do not have stingers, so they cannot sting.  The males merely fly around, buzz, and try to intimidate you into backing off, which usually works for me!  These wasps are, in a sense, both predatory and parasitic.  Female sand wasps catch other insects like flies and grasshoppers, paralyze them by stinging, and then bring them back to their nest.  Once in the nest, she lays an egg on the body of the paralyzed insect.  The hatched larva feeds on the “provision” until it pupates and overwinters.  Adult bees feed on nectar and are actually beneficial pollinators.

  To control yellow sac spiders (and a lot of other common house-dwelling insects like boxelder bug) we recommend the following exclusion and sanitation techniques:    
  remove spider webs, egg sacs, and harborage (clutter that provides hiding places)    
  frequently clean inside closets, attics, basements, and other storage areas    
  vacuum behind furniture, under baseboard heaters or radiators, in closets, and in other undisturbed areas    
  use caulking to seal cracks or crevices in the foundation or where pipes enter the house    
  install seals (weather stripping) around doors and windows that have large gaps    
  repair broken screens or windows    
  place sticky traps along baseboards or in other areas where spiders are seen    
Diadasia bee species (click here for more photos) have a very similar life history to the sand wasps.  One of the main differences, besides being bees instead of wasps, is that they provision their developing young with a ball of pollen.  Their nests are also slightly different in construction.  Diadasia species construct shallow burrows, usually topped off with turret-like protrusions made of mud.  The burrows lead to one or several cells at the end of different branches within the burrow.  Each cell at the end the burrow is lined with a secretion from the mother.

Because of sand wasps’ hunting and pollinating habits, and Diadasia species’ pollinating habit, both groups are considered beneficial.  In general, control is not recommended. In some cases, though, when large numbers of bees are located near your home, or if you or your children are allergic to stings, control measures may be warranted.  Because both of these genera like to make burrows in areas of exposed soil, one great long-term control is to plant a ground cover.  Ground covers should discourage bees/wasps from colonizing the same area the following year.  Another option is to simply fence off the colonized area and let them go about their business.  By observing their hard-working activities from afar, children (and parents) can learn about tolerating these beneficials.

If chemical treatment is desired, insecticidal dusts may be applied around individual holes.  The adult bees/wasps will pick up the chemical on their way in and out of the nest.  For safety reasons it is best to do this at night, preferably with the aid of a flashlight covered with red cellophane.  You should always wear long pants and long-sleeved shirts, and cuffs appropriately tucked in to prevent bees or wasps from flying into your clothing.  A head net should also be worn.  If you are allergic to bee or wasp stings, get someone else to do this for you.  Some chemicals that will work include carbaryl, bendiocarb, permethrin, pyrethrin, or diazinon.  Dust formulations will have the greatest effect.  It is difficult to eliminate all ground bees/wasps in one season.  If you do treat with chemicals, plant a ground cover the following spring to keep new bees/wasps from re-colonizing the area.

There are many species of ground nesting bees.  These two genera are only the tip of the iceberg.  If you find and collect ground nesting bees or wasps in your yard, please submit them to the UPPDL for identification.  If your ground nesting wasps are yellowjackets, control is usually warranted, and should be conducted very carefully.


-Ryan Davis, Arthropod Diagnostician