Ants translocate their larvae and pupae to a warm bird’s nest

Myrmica ruginodis translocates brood to a wood warbler's nest

In the nest of a wood warbler not only young wood warblers may grow up, but also ants, as Marta Maziarz and colleagues discovered. Ant larvae and pupae probably survive, grow and develop better in the bird’s nest than in their own nest.

Usually, nests of European forest ants, especially Myrmica ruginodis and Myrmica rubra (the European fire ant or common red ant), are so cold in spring that the larvae and pupae do not grow well. Their development only starts at 16°C, but ant nests rarely get that warm before summer. They are located on the forest floor, between fallen leaves of deciduous trees. The ants cannot produce heat, so without sunlight the nests have the same temperature as the environment. A temperature of 20 to 25°C is optimal for raising brood; the nests never reach that temperature in spring.

But warm places are available nearby, Marta Maziarz and colleagues show. On the forest floor, the wood warbler, a songbird that breeds in European forests, makes a domed nest of grasses, leaves and moss. The bodies of bird parents and, later on, their fully feathered young keep the nest warm.


When the bird parents incubate the eggs, in the second half of May, the nest temperature often reaches 16°C or more; especially on cold days, the difference with the ambient temperature is large. Once the young birds are fully feathered, in the first week of June, the nest temperature even rises to 20°C and higher.

This is a nice temperature for the ants, which indeed visit the warm wood warbler’s nest. In cold weather in May and in the first week of June, they move larvae and pupae from their own nest to a bird’s nest and put them in the sidewalls. Translocation is a lot of work, but apparently, it is worth the effort.

After fledging, the vacant nest cools down again. But the ants don’t remove their brood immediately; they delay relocation for up to two weeks. There is no hurry, because the bird’s nest is no longer warm, but it is not colder than the ants’ nest either.

In the primeval forest of Białowieża in Poland, where Maziarz conducted the research, the ants use 10 to 30 percent of wood warblers’ nests as incubators. The birds do not suffer from the inhabitants, but they do not benefit from them either. Therefore, they do not specifically seek the proximity of ant colonies when starting nest building. It is the ants that start the relationship and benefit from it.

Willy van Strien

Photo: Myrmica ruginodis with brood. Jan Anskeit (Wikimedia Commons, Creative Commons CC BY 4.0)

Maziarz, M., R.K. Broughton, L.P. Casacci, G. Hebda, I. Maak, G. Trigos‑Peral & M. Witek, 2021. Interspecific attraction between ground‑nesting songbirds and ants: the role of nest‑site selection. Frontiers in Zoology 18: 43. Doi: 10.1186/s12983-021-00429-6
Maziarz, M., R.K. Broughton, L.P. Casacci, A. Dubiec, I. Maák & M. Witek, 2020. Thermal ecosystem engineering by songbirds promotes a symbiotic relationship with ants. Scientific Reports 10: 20330. Doi: 10.1038/s41598-020-77360-z

New body

Loose head regenerates a complete Elysia sea slug

Elysia sea slug can grow new body from head

Sea slugs Elysia marginata en Elysia atroviridis can decapitate themselves and regrow a new body from the loose head, Sayaka Mitoh en Yoichi Yusa show. A bizarre phenomenon. Why do they do it, and how do they survive?

Sayaka Mitoh and Yoichi Yusa must have been dumbfounded when seeing sea slugs that they kept in their lab, species Elysia marginata, sever their heads from their bodies. The loose heads moved around, as they report. After a day, the wounds were closed. In some cases, especially in young sea slugs, things got even crazier: the head began to feed; after a week, a new body started to grow and in three weeks it was complete.

The loose bodies also moved for a while, sometimes even months, but eventually they decomposed. No new head appeared on any loose body.


There are more animals that can regrow a missing body part, such as a lizard that shed its tail or a fiddle crab that lost a claw. But this – regenerating almost an entire body – is very extreme. These sea slugs even have a groove behind the head as a predetermined breakage plane for self-decapitation. Why do they do it?

In any case, it is not to escape from a predator, like a lizard sheds its tail when a predator grasps it. The sea slugs take hours to separate body from head; that is not effective to avoid predation. And when the researchers simulated an attack by teasing them, nothing happened. The animals have a different defence mechanism against predators: they are poisonous.

The reason for self-decapitation became clear by observations on wild-caught specimens of a related species, Elysia atroviridis. Once in the lab, some of them shed the whole body, and these specimens turned out to contain a parasite, a copepod of the genus Arthurius. It is a large parasite that occupies almost the entire body of its host. In fact, a parasitized sea slug has already lost its body. If it sheds it, it will get rid of the parasite while losing almost nothing more.


But how does it survive without organs such as heart and kidneys? This has to do with a special property of sacoglossan sea slugs, to which Elysia belongs, the researchers suppose. They extract chloroplasts from algal food and incorporate them in special cells that line their highly branched digestive gland. The head also contains chloroplasts. Thanks to the chloroplasts, which they need to survive, these sea slugs can endure a period without food, it was known.

It is a mystery how exactly they utilise the chloroplasts. The chloroplasts continue to do what they do in plants: they convert carbon dioxide into carbohydrates with the help of sunlight, a process called photosynthesis. Whether the sea slugs can survive on sunlight as a result, just like plants, is a matter of debate.

Regardless, it may well be thanks to the chloroplasts that a loose head of Elysia marginata and Elysia atroviridis survives.

No eternal life

Parasitized Elysia sea slugs shed their worthless bodies. But they only manage to grow a new one from the head when they are young. The loose head of an older specimen does not feed and does not grow, but will die within ten days. Shedding and regrowing a body is not a recipe for eternal life.

Willy van Strien

Photo: Elysia marginata. Budak (via Flickr, CC BY-NC-ND 2.0)

The research explained on YouTube

Mitoh, S. & Y. Yusa, 2021. Extreme autotomy and whole-body regeneration in photosynthetic sea slugs. Current Biology 31: R233-R234. Doi: 10.1016/j.cub.2021.01.014
Wägele, H., 2015. Photosynthesis and the role of plastids (kleptoplastids) in Sacoglossa (Heterobranchia, Gastropoda): a short review. Aquatic Science & Management 3: 1-7. Doi: 10.35800/jasm.3.1.2015.12431

Collateral benefit

Bird disperses eggs of stick insects it swallowed

brown-eared bulbul disperses eggs of stick insects

Some stick insects are even more like plants than you might think at first glance. Just like plant seeds, the eggs can be dispersed by a bird, Kenji Suetsugu and colleagues show.

Stick insects are perfectly camouflaged: they do not stand out among the plants. Yet insect-eating birds are able to find them and will eat them. And that is the end of the story for such tiny animal.

Well, it may not be, Kenji Suetsugu and colleagues report. If an unfortunate female stick insect is carrying mature eggs, a few of these appear undamaged in the bird’s droppings, and some may even hatch.


The researchers, working in Japan, point out that the eggs of stick insects resemble plant seeds: they have the same size and colour and feel the same thanks to a hard shell. Hence their suggestion that the eggs might survive passage through a bird’s digestive tract like plant seeds do. Many plant species produce fruits that are eaten by birds or other animals; the seeds remain intact, are excreted and germinate. Is something similar possible for the eggs of stick insects?

eggs of stick insect after passage through a bird's digestive tractTo find out, they mixed mature eggs of three stick insect species with an artificial diet and fed this to a brown-ear bulbul, one of the main predators of the insects. Afterwards, they examined the bird’s droppings under a stereomicroscope and discovered a small number of intact eggs, and from some of these eggs a young stick insect hatched later on.

Such scenario is also possible when a bird swallowed a gravid female, the authors think. The youngsters that hatch after passage through a bird’s guts would have to find an appropriate food plant to live on, but that is always the case. Normally, a female just drops her eggs to the ground and does not provide any care.


young stick insect, hatched from egg that passed through a bird's gutsSo, sick insects not only look like plants, but they also exhibit a surprising plant-like trait: dispersal of offspring by birds, which is unique in insects.

Dispersal by an avian predator is only possible for species that reproduce parthenogenetically, for in that case females carry eggs that can develop without fertilization. A number of stick insect species exhibit parthenogenesis, including the species that were studied here.


Dispersal of insect eggs via a bird’s digestive tract is not entirely comparable to dispersal of plant seeds. Plants produce fruits that have to be eaten to disperse their seeds. In contrast, a female stick insect has no intention to be captured by a bird to have her eggs transported – by being camouflaged, she tries to prevent just that. But if she is unlucky enough to become a bird’s meal, it is a collateral benefit if some eggs survive and young hatch, if only a few.

The hard eggs probably have not evolved to facilitate avian dispersal, the authors suggest, but to decrease the risk of attack by parasitoid wasps, which lay their eggs in other insects’ eggs.

Stick insects are immobile. Thanks to the birds they may reach new places to live. An interesting question is whether distribution patterns in the insects, to be unravelled by DNA research, overlap with birds’ flyways; that would strengthen the idea that the eggs are sometimes dispersed like plant seeds.

Willy van Strien

Large: Brown-eared bulbul (tongue visible). Alpsdake (Wikimedia Commons, Creative Commons BY-SA 4.0)
Small: stick insect (Ramulus irregulariterdentatus) eggs that passed through a bird’s digestive tract and a young stick insect that hatched from such egg. ©Kenji Suetsugu

Suetsugu, K., S. Funaki, A. Takahashi, K. Ito & T. Yokoyama, 2018. Potential role of bird predation in the dispersal of otherwise flightless stick insects. Ecology, online May 29. Doi: 10.002/ecy.2230

Nutritious two-component glue

Queen larva is firmly attached to her ceiling

Royal jelly, fed to a queen larva, holds her in place

A bee larva that is to become a queen receives large quantities of royal jelly. And that is not only because the stuff is nutritious, as Anja Buttstedt and colleagues show.

A female honeybee larva can become a worker or a queen, her fate depending on the food she receives. During the first days, all larvae are treated to the so-called royal jelly, a nutritious mixture that the nurse bees produce in their head glands; it is rich in proteins, sugars and fats. After the third day, larvae that will grow up to be worker bees are raised on a different diet. When they pupate, nurse bees close their cells with a layer of wax. But a larva that is destined to become a queen is fed on royal jelly exclusively; the nurse bees bring it to her in generous quantities. Thanks to that nutritious diet, she grows bigger than worker bees.

Queen cup

The royal jelly has still another function, Anja Buttstedt and colleagues discovered: it holds the queen larva in place.

And that is badly needed. The cells in the comb, in which worker larvae grow up, are too small for a developing queen larva. For her, the bee workers will build a special cell, a so-called queen cell or queen cup. It is not only wider, but also differently oriented: vertically, opening downwards. Therefore, her royal highness could easily fall out of her cell.

Buttstedt shows why that does not happen: the royal jelly, which the workers deposit on the ceiling, is so sticky that it keeps the larva hanging from the ceiling until it pupates and the cell is sealed with wax. The stickiness arises because two proteins, royalactin (the main protein in royal jelly) and apisimin, form long fibrous structures that make the jelly viscous.

Fiber network

The workers produce and store the proteins in their hypopharyngeal glands. The gland mixture is liquid, enabling the bees to excrete it. But when they deposit it in a brood cell, they combine it with fatty acids which they produced in the mandibular glands, and in those acidic conditions, the proteins royalactin and apisimin form a fiber network.

So, royal jelly is a two-component adhesive, as the authors conclude, serving as excellent food as well. It is just what a queen larva needs to grow up safely.

Willy van Strien

Photo: Honeybee, comb and two queen cells. Piscisgate (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Buttstedt, A., C.I. Muresxan,H. Lilie, G. Hause, C.H. Ihling, S-H. Schulze, M. Pietzsch & R.F.A. Moritz, 2018. How honeybees defy gravity with royal jelly to raise queens. Current Biology, online March 15. Doi: 10.1016/j.cub.2018.02.022