One month ago a fellow bird dog training club member discovered tiny brown bugs infesting grain he stored in his garage to feed our club pigeons. He thought I might like to determine their name and report on their natural history. "Sure," I said, so he presented me with several dozen live bugs in a plastic medication vial. He did an Internet search himself hinting to me these 3-4 millimeter-long bugs might be grain weevils.
With help from the "Peterson Field Guide-Beetles" and "The Natural History of Insects" (1996) by Rod and Ken Preston-Mafhan I learned the distinguishing characteristic of these bugs was six legs making them insects. Since they had a horny firm covering over their abdominal segment, segmented antennae and chewing mouth parts, they had characteristics of beetles. Beetles have been the most successful of all animals for survival and for sheer number of species on Earth since over 350,000 species have been discovered in every conceivable climate on every continent. Three features have contributed to successful growth and survival of beetles. First, small size, usually less than 1 centimeter, permits feeding and hiding under fallen leaves and trees and in grass. Second, the beetle body covering called an exoskeleton provides protection and preserves body moisture. Finally, the diet is variable since every living or dead plant or animal is eaten by some species of beetle.
Under magnification the specimens I received revealed a long narrow turned down snout categorizing them as snout beetles. The presence of segmented antennae attached to an elbow and wing covers extended to the tip of the abdomen further identified them as grain weevils as described in the "Peterson Guide" since they did not fly whereas the similar maize and rice weevils could fly. Our weevil did not fly. So, my friend got it right, I think.
So what makes a beetle a weevil? Webster's Dictionary defines a weevil as a beetle which feeds on grain, fruit, nuts, plant seeds or cotton bolls.
Therefore, I assume a weevil is not defined by specific structure but by the fact it eats valuable agriculture crops becoming a pest hence labeled derogatorily, a weevil. The most notorious weevil, the cotton boll weevil, discovered in Texas in the early 1900s, caused farmers to lose millions of dollars from lost harvest annually when the weevil destroyed the cotton flower which produced the cotton fiber. While the vast majority of beetles are beneficial since they eat dead and decayed plants and animals or eat other insects, a weevil is considered an evil beetle.
Since the beetle specimen I studied eats grain, it is a weevil and weevil life cycle involves metamorphosis. After mating the female lays eggs in grain by chewing into the seed. Eggs hatch into small caterpillars which consume the grain, shedding their outer layer several times to accommodate growth and emerging from the last shedding as adult weevils ready to reproduce. The life span of most weevils is only several months.
Since insects have six legs, have you ever wondered how they move with out kicking or stumbling on their front legs? Keen observers noticed insects, including beetles, moved by raising the right front leg, left mid leg and right rear leg at the same time leaving the other legs on the ground creating a tripod stance. The legs on the ground pushed the insect forward until the other three legs touched the ground repeating the cycle. As a general characteristic, insects have wings, beetles included. Outer wing covers are opened and held stationary like airplane wings while the membranous wings underneath flap forward and down 100 times per second to produce flight. The grain weevil I studied is unusual because the outer wings are fused closed and vestigial wings underneath are incapable of flight.
My dog training friend sent me an evil beetle, a weevil, which in this case proved to be profitable since I gained a greater understanding of our natural world. Weevils are ubiquitous, a bit creepy and present man with a never ending challenge to protect agriculture crops around the world.