Excluding those insects which need a blood meal to complete their life cycles, many insects and spiders can bite but usually only do so when they have become trapped and perceive you as something other than scenery. Judging from some of my bites, I also suspect that some (especially ants and spiders) have adopted an exploratory procedure called ``I'll test this and see what happens''. Occasionally, under the right circumstances, you, or rather some small part of you such as a finger, may be perceived as prey.
Stings usually occur when an insect like a wasp, hornet or bee gets trapped. Since most of us recognize the potential of these insects, such trapping is usually accidental. (I say ``most of us'' because I did recently have an adroit little boy capture a bumble bee in one of the bug boxes.) As a child, it took me several painful summers before I consistently associated the clover blooming on my grandfather's lawn with active honey bees. Normally stinging is used only as a last resort because the insect is temporarily defenseless when the venom is used up. In the case of the honey bee, the bee dies.
A number of insects, including the harlequin bugs and the so-called stink beetles, will spray. Recently, when I got too close, a 1/2" long leafhopper resting on sweet fennel turned its abdomen towards me and squirted a couple of droplets of something. These droplets didn't go far but I did retreat. Sprays vary in toxicity. If you are not sure about an insect you might do well to keep your eyes away from insect behinds. Since staring an insect eye-to-eye can be regarded as a threat, watch out for a change of orientation or better yet just keep a respectable distance.
In addition to these active defenses, many insects (especially caterpillars) and spiders (including tarantulas) have passive ones in the form of small hooked and barbed hairs that can come off and be very irritating. (Those of you who have handled fiberglass without gloves know how irritating such fibers can be.) If you must handle these creatures, keep them on the tougher skin like the palms of your hands.
It is possible to violate an insect's space and like us this varies from individual to individual and situation to situation. Bees, for instance, are sometimes less tolerant of disturbance during and right after poor weather especially if it affects their ability to gather nectar and pollen (they become cranky). Under these circumstances, some aggravated insects will fly right at your face whether or not they can sting. Tolerance around nest sites is unpredictable (a number of factors are involved in the perception of threat including recent disturbances, your activity and the size of the nest). On the other hand, some insects, even excellent flyers such as dragonflies, have been known to fly into people, apparently accidentally.
Remember, some people, perhaps even you, become very uncomfortable in the presence of certain insects, especially bees and wasps. Even if they can't be seen, they can still be heard. Since we respond differently to bites, stings, sprays and other irritants, it is only through trial by fire that we learn about our bodies sensitivities, sometimes with unfortunate consequences.
With the expected arrival of the africanized honey bees in San Diego within a year, everyone's insect awareness will soon take a quantum leap. As winter approaches and bug activity diminishes, now is a good time to develop your awareness.
Enjoy the bugs and, in the process, don't stand on any ant hills for long.
Ron Lyons (volunteer 1990-1999)