When asked what we might infer about the mind of a hypothetical creator of life on Earth, renowned biologist J.B.S. Haldane famously replied, "a great fondness for beetles." More than 350,000 species of beetles exist, and 40 percent of all insects are classified as some type of beetle. Even with so many species of beetle adapting to their environments, none has evolved a stinger. Beetles do not sting. There are species, however, who have evolved strategies for self-preservation, some potentially bothersome to humans, but none very dangerous.
Stag beetles get their name from their menacing branching mandibles, which resemble the antlers of a stag. These mandibles evolved for combat among male beetles for mates. Stag beetles are capable of biting through human skin, but the bites rarely cause more than minor discomfort and heal easily, resulting in no serious damage. These beetles are not considered pests, but actively support forested environments by helping decompose dead wood. In Japan, they are considered harmless and interesting enough that their rearing has become a popular hobby.
Blister beetles are so named for their ability to to produce blistering on human skin. The blistering is caused by their hemolymph, which adult blister beetles produce in quantity when pressed or rubbed. The blisters often appear on the arms or neck. While they cause discomfort, these blisters are rarely painful, and usually require no treatment other than basic first aid and heal on their own. These beetles are attracted to outdoor lights at night, but mere contact is unlikely to result in hemolymph release and subsequent blistering.
The African bombardier beetle possesses perhaps the most impressive defense evolved by a species of beetle: a toxic, boiling hot liquid that sets off a loud, explosive sound when fired. These beetles' aim is nearly perfect in all directions, making them a formidable nuisance. Fortunately, the bombardier beetle is no major threat to humans. Though its liquid can burn and irritate the skin, it does not cause major damage; it is, however, devastating for the predatory ants against whom it evolved. This defense mechanism is so sophisticated that bombardier beetles are often cited as evidence for creationism.
Flesh Eating Beetles
Also known as dermestids, these beetles live on carrion, and are often found in large quantity feeding on animal carcasses. They are not known to feed on living flesh or pose any direct danger to humans, though they can become pests and infest areas where dead animal flesh is left exposed. Due to their efficiency in stripping the flesh off the dead, flesh eating beetles are often used by museums to "skeletonize" dead animals. They have to be watched closely, though, or their insatiable appetites will lead them to devour dead skins, leather, and paper.