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Bug of the Month March 2019


Spiders are friends in the field

by Prof. Dan Johnson, University of Lethbridge

Natural enemies of insect pests perform a great ecosystem service and therefore deserve of efforts to conserve them, or at least not actively kill them. We often forget one of the most important groups of organisms that tirelessly battle insects that feed on our crops, on forests and even on ourselves.

Wolf spider

All things come to he or she who waits. If not, run it down – the gospel according to wolf #spiders. This wolf spider (Schizocosa) is eating a velvet-striped grasshopper, (Eritettix simplex).

Hundreds of species of spiders spread out in populations of thousands to hunt and destroy insects, including those that increase in numbers in response to the encouragement provided to them by crops and urban plantings. Spiders present essentially no personal risk to us in Canada. Even nations like Australia, where the dangers are legendary, go years and years with no fatalities from spiders, although the same cannot be said about the risks from bees, wasps, dogs, horses, wildlife, and even dust mites, all of which have tallied more significant body counts worldwide.

jumping spider
Jumping spiders have complex behaviour that seems intelligent, even curious.

Maybe the reason we ignore spiders, and sometimes fear them, is because we have not seen them up close enough to appreciate their various forms, interesting activities and contributions. The group called the jumping spiders, for example, have behaviour that is complex and seems intelligent, even curious. Orb weavers, which are often noticed sitting fat and patient in their webs, have been seen in increasing numbers in recent years.

running crab spider

Running crab spiders, like this one, and wolf spiders chase down their small prey.

They are famously good at capturing flying insects, while the funnel weavers use webs closer to the ground to do the same, sometimes covering grassland with shimmering webs that also catch the light. Crab spiders wait in the vegetation and grab unwary prey insects, while spiders in other taxonomic families, like running crab spiders and wolf spiders, chase down their small prey. Spiders have maintained their numbers and activities through thousands of generations since the ice ages ended, and will continue to keep up the work of turning over the food webs, running ecosystems, and greatly reducing our partially self-imposed pest problems. The good news is that they are adept at adapting to changing climate and opportunities.  The poster below will give you a start on recognizing some of the different types, and names of typical taxonomic families.