Over the last few weeks, as communities across New England witnessed a meteor shower and a rare aurora borealis, one more auspicious event was overhead – swarms of ants took flight – and covered the sky (as well as vehicles, porches, and sidewalks).
While state agencies were alerted and complaints exploded on social media, the panic was an unnecessary reaction to a harmless annual event: ants meeting up to make more ants. That’s right, ant sex was everywhere, and it was not demure at all. To help make sense of what we witnessed and how special it was, we will have to start with the birds and the bees.
Biologists have no common definition of sex. The phrase “biological sex” is spoken about far more by trolls online than in any biology textbook or lecture hall. It is a myth because the attributes of sexually reproducing organisms vary across many phenotypic axes, including anatomic, genetic, developmental, transcriptomic, endocrine, psychological, and behavioral spectra. The amount of variation we can measure among individuals, whether for hormones or body size, is often greater than between any binary classification scheme. What’s binary are our gametes, eggs and sperm – and it’s their fusion (through sexual activity or by assisted reproductive technologies) that can lead to the growth of a new, diploid individual with two sets of genetic information. Many ants develop following this pathway, but not all.
Ants are extraordinarily numerous, and their abundance averaged >80% of all arthropods collected in a campus survey at Providence College. Most of these, however, are sterile and wingless. The normal ant we’re most familiar with is commonly called a female worker and is diploid, like us, developing from the fusion of an egg and a sperm cell. Queens or mother ants can decide when to fertilize and lay their eggs, having retained a cache of sperm from their mating flight. In most cases, workers develop without ovaries and without an ovipositor. It is modified from an egg-laying tube into a venom stinger or formic acid sprayer. So, who were the ants flying overhead? When the same fertilized “female” eggs are fed a different diet, which happens roughly once a year, they can develop into new queens, often with a much larger body, two pairs of wings, and lifespans 100x longer than their worker sisters. Remarkably, if an unfertilized egg is laid, it develops into a “male” ant, which can bring the sperm to the mating flight party. So, there are probably at least three common sexes among ants, and we haven’t even mentioned gynandromorphs or some of the more complicated sex determination systems. Shortly after mating, the males die, but the newly mated queens rip off their wings, start digging new nests, and transform into new mothers. As for humans, the genetics ants inherit at birth are only the start of a lifetime of diversity in form and function. We don’t know the seasonal cues that send new queens and males into the sky; however, for many, like the open-field nesting Labor Day ants, which recently flew, it’s a seasonal event we can look forward to every year. •
Illustration by Danika Valentine. Follow Dr. Jane and her Providence College research lab on Instagram @antlabpvd or on the web at www. lovetheants.org.
