Sunday, January 10, 2016

Crab Spiders

 Each fall local gardens are invaded by crab spiders, also known as spiny-backed spiders.  There are two species of crab spiders on the Big Island of Hawaii, both are shaped like tiny crabs approximately ½ inch across. One is white with black spots and 6 red spines. The more common one also has spines, although shorter, with two distinct white spots on its speckled yellow-brown back. In certain locations, crab spider populations increase in the fall and decline in the late spring.

These spiders are different from other spiders in their web building techniques. Their webs are interconnected, building condominiums right outside your door, under the eaves, between the shrubs and in the trees.  They seem to be spun everywhere, but the spiders are not a nuisance indoors. 

People, especially farm workers, have been bitten when the spiders fall on them or are trapped within their clothing. Females lay eggs away from their webs, on the leaves of trees and elsewhere. The egg masses look like a flat patch of fluorescent green cotton candy which turns yellow when the eggs hatch. Disposing of this egg mass will, of course, help to reduce the spider population.

Spiders, including the crab spiders, are some of the best bio-control agents known, because they feed on large quantities of insects such as aphids, ants, thrips and termites. They should be tolerated as much as possible. But, people do have their limits. A soap and/or oil solution will kill them. In addition, many household, aerosol insecticides will do a good job of killing the spiders. Before using, read the label for precautions and application sites. Note: application to plants may cause severe burning.