On a recent trip to research insect populations, I visited a small sliver of the Chihuahua desert that runs through the extreme southeast corner of Arizona. While hiking through the flat expanse, I encountered hundreds of eager hover flies. I say eager, because the flies followed and buzzed around me relentlessly. While I couldn’t identify any single individual fly, I am certain that a few of them followed me for more than half a mile as I trekked through the dry, rock strewn, dusty desert. I am not a dancer, but all of the swatting, arm waving, and stumbling probably made me look like I move like Mic Jagger. Relief came when wind from an approaching thunderstorm forced the flies to land or be blown away.
Of course, the flies were after me because I was a source of water and salt in the middle of a desert. The flies need both to survive and reproduce, and with a life span measured in weeks, the flies had no time for politeness. Their tiny biological clocks were ticking. They were in their golden days, having already lived most of their young lives as larvae and then metamorphosing into the annoying fly stage that zipped just a little too close to my ear canals. For me it was irritating, but for the swarming flies, it was all-or-nothing; do or die.
Insect Bias
As a group insects get a lot of bad press, when they get any at all. Biting and stinging insects of course figure prominently in many stories. There are a number of published articles headlining that insects make up a significant number of invasive species, which is partially true, but the biases against our chitin covered earthmates are largely out of proportion. Why is large group of caribou called a herd, but a large group of insects is a swarm. Swarm has a more sinister, negative connotation. Swarming hover flies are pests. While many people mourn the loss of the huge buffalo populations that use to wander the western prairies, if hoverfly populations dropped significantly, no one would likely invest in a hover fly reintroduction program. Insects are not generally considered a charismatic species, meaning they don’t draw the attention that elephants and polar bears garner. No one pines for the years when painful, stinging harvester ants were more plentiful in east Texas. No one has established a non-profit to reintroduce the rocky mountain locust, whose past populations inspired the following letter from E. Snyder of Highland Kansas:
At our place they commenced coming down about 1 O’clock in the afternoon, at first only one at a time, here and there, looking a little like flakes of snow, but acting more like the advance skirmishers of and advancing army; soon they commenced coming thicker and faster, and they again were followed by vast columns, or bodies looking almost like clouds in the atmosphere. They came rattling and pattering on houses, and against the windows, falling in the fields, on the prairies and in the waters – everywhere and on everything. By about 4 o’clock in the afternoon, every tree and bush, buildings fences, fields, roads and everything, except animated beings, was completely covered by grasshoppers.
The disappearance of the locusts that terrorized the American frontier is noteworthy in that it happened to an insect pest that, at the time, no one believed was vulnerable to extinction. Why? Because insects appear to be so numerous, it is difficult to imagine them being eradicated. They are described as “R” selected, meaning they have short lifespans and produce enormous numbers of offspring, among other traits. Such characteristics may seem to make insects invincible, but the truth is many insects are especially vulnerable to habitat loss and invasive species. Even if insects produce a large number of eggs, they usually have specific habitat requirements necessary to ensure survival.
Declining Populations
An article in Science (May 12, 2017) reports that insect biomass captured in traps spread across more than 100 European nature reserves has dropped dramatically since the 1980’s. Members of the Krefeld Entomological Society, a group of amateur entomologist that have been monitoring insect abundance, raised concern after comparing earlier masses of insects trapped to those in 2013. Whether similar declines are happening in other locations around the world is difficult to say, because there are too few surveys across multiple years to make anything stronger than a guess. Also, insect populations can vary significantly from one year to the next, in cycles that may last several years to a decade. So even if annual surveys were available, for some insect species, it still wouldn’t be enough. Finally, the lack of public awareness concerning the extinction risk of many insects, other than honey bees and monarch butterflies, means there is likely insufficient funding to conduct surveys. More recently, a group of researchers reviewed166 long-term surveys of insect assemblages across 1676 sites looking for trends in insect abundances over time. They found that there were declines in terrestrial insects, but increases in freshwater insect abundances.
So why be concerned about declining insect populations? Because they pollinate most of our food crops, aerate the soil, control other pests, and feed those bat, bird, and fish species we humans so love to photograph.
