From the Field

One day, I spotted a curious-looking structure on the wall of my house. On close examination, turned out to be a wasp building a house – a nest made of mud, rather. It was hard to believe that one wasp was single-handedly building the nest. Thus started my interest in potter wasps which led me to my research on the group in the Indian Institute of Science (IISc).

Delta pyriforme

The builders

All wasps belonging to the subfamily Eumeninae (Family: Vespidae) are called potter wasps. They are diverse and Kumar et al. (2019) report that there are 189 species belonging to 47 genera recognised from India. The larger potter wasps with a body length of 30 mm are easier to track and I have been able to watch the beautiful Tiger Potter Wasp (Phimenes flavopictus), Delta conoideum and Delta pyriforme build nests.

Phimenes sp. with a bolus

Delta conoideum

The ground plan

On bright sunny days, wasps fly about, exploring soil and surfaces by tapping their antennae to ensure that conditions are favourable for nesting. They generally choose places sheltered from direct sunlight or rain but a few nests have also been seen exposed to the vagaries of nature. Even though exposed, they never develop a crack, protecting the life being nurtured inside.

The process of nest building begins with the wasp carrying a few droplets of water in their mouth to the soil. They mix them up, fabricating tiny mud balls called boluses, which are carried to the selected nest site. With rapid movements of the mouth parts and forelegs, they flatten the mud which dries out due to the ambient temperature and remains intact.

The steps are repeated throughout the day with regular tapping and walking over nests for inspection. A fully made compartment of the wasp home would include a mud chamber with an opening of about 2 mm size, complete with a lip which would make it suitable for the wasp to perch while laying its egg. A single egg is laid into the chamber after which the mother flies away in search of caterpillars to provision inside the nest. Once a nest is complete, the mother leaves in search of a new site to start building again.

Behind the scenes

The role of the male is limited to mating and the entire responsibility for house construction and food provisioning lies solely on the female. The male leaves no stone unturned in conveying his intentions as soon as he emerges – waiting outside his own nest for sisters to emerge to engage in mating!

Stocking the larder

Potter wasps provision nests with paralysed caterpillars belonging to the lepidopteran families, Noctuidae and Geometridae, and beetle families, Chrysomelidae and Curculionidae (Kumar et al., 2019). Each chamber is provisioned with a variable number of caterpillars ranging from three to seven. The number of caterpillars provisioned inside each chamber would also depend on the sex the egg will turn into – eggs giving rise to male wasps would require lesser nutrition and hence a lesser number of caterpillars as opposed to females who would need more.

Nest with caterpillar

Insect intruders

Many-a-things can go wrong for the mother wasp building a nest. She can have an accident or get eaten by a predator which would mean that the nest would remain incomplete. Opportunistic insects sneak in to lay eggs while the hapless mother is away. Chrysididae wasps or Cuckoo wasps, many flies and different parasitoid wasps lurk in the dark waiting to capitalize when the mother wasp flies off looking for food.

Cuckoo wasp

The eggs of the parasitoids always hatch faster than that of the potter wasp so that they can feed upon the provisions and emerge soon. Some intruder flies and wasps fail to break open the mud structure and die within the nest en masse. Often, Velvet ants (Family: Mutillidae) are seen near mud nests looking to make a breach.

Mutillid ant looking to breach the nest

Time-bound construction

Building structures takes time but a potter wasp roughly takes a day to build one chamber. Finding food to provision is what takes more time and the wasp spends anywhere from 20 minutes to an hour or two to find a caterpillar. After the nest is complete, it takes around 22-27 days for the first adult wasp to emerge and subsequently in a week’s time the entire lot emerges. The presence of exit holes reveals that the nest is empty. Empty potter wasp nests are homes for a whole different set of organisms; spiders, mites, and sometimes lizards use them to lay their eggs.

Nest lodges

Why spend energy building nests when empty wasp nests are readily available? The Sphecid wasp Chalybion sp. often finds a suitable empty nest to re-use. She simply cleans the inside of the nest, provisions it with new food and seals the exit holes with a whitish material (the source of which is still unclear). She even lays extra white material on the nest possibly to confuse potential predators about the exact location of the nest entrance.

Myriad surfaces, shapes and sizes

Stone walls, concrete walls, glass windows, rubber handles, unused scooters, tree barks, plant stem and many other surfaces are chosen as surfaces to build homes.

Nests of different shapes and sizes adorn our walls and attics- ranging from simple single pots to multiple pots. It is not unusual to find many mud pots, fortified further by more mud to form a firm mound-like structure. With an eye for aesthetics, when conditions are favourable, wasps spend hours decorating their simple mud homes with different materials.

Decorated mud nest

The wise old wasp from the chapter titled ‘The Wasp in a Wig’ from Lewis Caroll’s ‘Through the looking glass’ gives life lessons to Alice. Though the chapter never saw the light of day, potter wasps teach us a thing or two about architecture and eco-friendly construction. So, let’s not callously break the next mud nest we see, and instead appreciate the craftsmanship of these creatures.

References

Girish Kumar P., Pannure A., and Carpenter J. M., 2019. Potter wasps (Hymenoptera: Vespidae: Eumeninae) of India. In Indian insects- diversity and science. Eds. Ramani S., Mohanraj P. and Yeshwanth H. M. 445pp.