Dear Old Dad!

Features - Insect Behavior

In honor of Father’s Day this month, new research showcases the best and brightest fathers of the insect world.

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June 8, 2020

©Rick Sargeant | Adobestock;

Editor’s Note: This article originally appeared in Entomology Today, a project of the Entomological Society of America with the goal of reporting interesting discoveries in the world of insect science and news from various entomological societies. To learn more, visit www.entomologytoday.org.

Dads often get a bad rap in the animal world. While it’s true that mothers typically do the lion’s share of childrearing across species, there are some exceptions to that rule in the form of devoted dads. To celebrate Father’s Day this year, we have compiled some fascinating insights on exceptional paternal care in the insect world as recently discovered through entomological research.

GIANT WATER BUGS. One of the most classic examples of paternal care in insects is the giant water bug. In these animals the traditional mother and father roles are reversed, with females actively searching for males to mate with and males rearing the young. Female giant water bugs lay their eggs on males’ backs, after which the males are solely responsible for caring for the eggs until hatching. Males can mate with multiple females, adding eggs to their backs until no space remains.

Researchers collected adults of the giant water bug species Diplonychus rusticus to test whether females are differentially attracted to males with or without eggs on their back. When introduced to a group of males where half had 10 eggs on their backs and half had none, female giant water bugs preferentially laid eggs on males that already had eggs on their backs instead of egg-free males. This result led to the conclusion that paternal care is under sexual selection in Diplonychus giant water bugs, with female preference for egg-caring males resulting in increasingly caring males over time. These little guys take piggyback rides to a whole new level!

Lethrus apterus beetle fathers guard their underground broods against intruders.
©Sergei Bykovskii | Wikimedia

BEETLES VS. INTRUDERS. The best fathers protect their clan, as Lethrus apterus beetles do when confronted with intruders. This biparental species raises subterranean broods, and while the mother beetle tends and feeds young below ground, the father guards the tunnel entrance against males who seek to take over the burrow. A study looked at how the size of conspecific intruders affected the outcome of battles with a guarding male. Through a field experiment conducted in Hungary, researchers found that larger intruders are quicker and more likely to engage in fights with guarding males than smaller intruders, and are more likely to win.

However, despite their advantage over smaller competitors, larger intruders still did not fare well against guarding males, as the home beetle nearly always successfully defended its territory. The study authors hypothesize that guarding males tend to overcome intruders because they have more to lose: The motivation to protect an established family and home is stronger than the intruders’ guile to overtake a burrow of unknown quality. For these beetle fathers, home is where the heart is, and that’s something worth protecting.

BURYING BEETLES & CORPSES. Burying beetles have one of the most elaborate and well-known biparental care systems in the insect world. Together, male and female burying beetles bury a small vertebrate corpse in the ground and then rear offspring within the crypt, feeding their offspring and themselves with the carcass meat. The fathers also defend their brood against rival beetles and other intruders. Interestingly, male burying beetles that have previously raised a brood have been found to emit higher levels of sex pheromones and subsequently attract triple the number of females than are attracted by males that haven’t bred yet.

Beetles: ©Calle Eklund | Wikimedia;
Vertebrate corpse meat provides burying beetle fathers with the energy needed to rear multiple broods.

The scientists behind that discovery recently decided to examine the potential underlying causes of that pheromone boost. They found that Nicrophorus vespilloides burying beetle males that raised a brood and fed on a vertebrate corpse emitted higher amounts of sex pheromone than unbred males that fed upon dead invertebrates. The authors concluded that increased pheromone production by burying beetle fathers is likely driven at least in part from the high-quality vertebrate carrion upon which they are able to feed during brood care. Meaty carcasses thus play double duty for burying beetle fathers, fueling them through brood care and beyond to when they search for another female with which to start a family.

FLY COURTSHIP SONGS. Before becoming fathers, males need to find a mate. In many insect species, males have developed elaborate methods with which to attract females, such as the courtship songs that Drosophila fruit flies conduct through wing vibrations. Recently, researchers investigated whether the type of host cactus on which two different Argentinian Drosophila species were raised would impact their courtship songs. Drosophila buzzatii uses prickly pear cactus as its host plant, while Drosophila koepferae uses columnar cacti. The two species also differ in the purpose of their courtship song: D. buzzatii relies on song for mate recognition, while D. koepferae uses song to communicate mate quality, relying instead on chemical cues for mate recognition.

With these differences in mind, the researchers expected D. buzzatii’s song to stay the same regardless of host cactus because mate recognition depends upon a stable signal irrespective of environment, while D. koepferae’s song would differ because nutritional differences in the type of host cactus would lead to song variation that reflected male quality. This is exactly what they found, with D. koepferae’s song changing structure and increasing in volume when raised on the nutritionally superior prickly pear instead of columnar cactus, while D. buzzatii’s song stayed the same regardless. These results show the important role host plants can play in the divergence of sibling species, and the fascinating courtship methods that can subsequently develop in fathers-to-be.

©yb_woodstock | Wikimedia
Male fireflies adjust their courtship flashing signals to ensure females notice them.

MALE FIREFLIES. Sometimes it’s the flashiest guys who get the girls, and this is especially true in the case of fireflies. In urban areas, though, nighttime light from human development threatens to outshine even the brightest firefly. Investigators recently sought to discover whether male fireflies might be able to increase the brightness of their courtship flashes in the face of interfering light pollution. To find out, they exposed varying wavelengths of light to adult Aquatica ficta males, a common Taiwanese firefly that maintains small populations within the bustling metropolis of Taipei.

Typically, A. ficta males produce intermittent, one-second-long yellow-green flashes to attract mates. When exposed to short- and mid-wavelength light at dim intensities, however, the fireflies emitted brighter flashes at a less frequent rate. Short- and mid-wavelength light at bright intensities often caused fireflies to cease flashing entirely, likely because it induced daytime inactivity in the fireflies, while long-wavelength red light had no effect on flashing regardless of intensity. The researchers concluded from this data that male A. ficta fireflies are unaffected by longer wavelengths of light, while shorter wavelength light spurs them to increase the conspicuousness of their flashes to ensure visibility to females. These insects truly shine in their quest to become fathers.

Whether through flashy courtship displays or fantastic childrearing skills, insect fathers go to great lengths to produce offspring and continue their species’ longevity. Happy Father’s Day to insect and human dads alike!