Whoever Digs a Pit, or a Few Words About the Antlion
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The following article was originally published in the journal for educators Biologia w Szkole (eng. Biology in School) (1/2023):
We can identify a wide range of strategies used by heterotrophic organisms to obtain food. One of these is predation, often defined as a mode of nutrition that involves consuming the body of another animal as food. It is important to note that, unlike parasitism, predation results in the death of the prey. From an ecological standpoint, this strategy is classified as one of the antagonistic interactions, which may be interspecific or intraspecific (cannibalism), and which have evolved through mutual adaptation, providing a clear example of coevolution. Along with other forms of interspecies interactions, predation plays a major role in shaping ecosystem structure [1] [2].
For potential prey, becoming a food source is clearly disadvantageous, which is why many species have evolved numerous ways to avoid this fate. Unsurprisingly, predators have in turn developed a variety of hunting strategies, whether hunting alone or in groups, to overcome these defenses.
When we think of predators, we most often imagine animals. However, this nutritional strategy is also present in other groups of organisms: certain plants (like carnivorous sundews Drosera and Venus flytraps Dionea), specialized fungi (Stylopage grandis, Arthrobotrys oligosporus, among others), and even microorganisms such as the large amoeba Amoeba proteus.
Some animals capture their prey while in motion. Such chases may be fast but are usually short, and if the prey is not caught almost immediately, the predator often abandons the pursuit, as seen in the cheetah Acinonyx jubatus. Other species rely on longer pursuits in which the exhaustion of the prey is the decisive factor, as in the gray wolf Canis lupus. Ambush hunting is another widespread strategy, exemplified by the northern pike Esox lucius.
A chase is not the only predatory method. Some predators capture their prey using a quick strike of the tongue (frogs Anura, chameleons Chamaeleonidae) or with stinging cells (cnidarians Cnidaria). Another relatively frequent method involves building traps of various kinds. One of the most well-known examples is the spider's web Araneae.
Far less often mentioned, at least among trap-building predatory animals, are the antlions Myrmeleon. Their very name, in both Polish and Latin and ultimately derived from Greek, combines the words "ant" and "lion," which makes it especially intriguing. Let us therefore take a closer look at these fascinating creatures.
Antlions
Antlions Myrmeleontidae are the most species-rich and widely distributed group of net-winged insects Neuroptera.
Net-winged insects represent a group of approximately 6,000 predatory species that undergo complete metamorphosis. They are characterized by transparent wings with rich venation. Together with snakeflies Raphidioptera, alderflies, dobsonflies, and fishflies Megaloptera, they form the clade Neuropterida [3].
Antlions are closely related to owlflies Ascalaphidae [4], and the larvae of both families share numerous morphological similarities.
The earliest known antlions appeared around 130 million years ago, during the early Cretaceous period [5].
This family includes the largest known lacewing species. Adults have two pairs of large wings, each reaching up to 80 mm (3.15 inches) in length, with a wingspan of about 60 mm (2.36 inches) [6]. Their body shape and appearance strongly resemble dragonflies Odonata. However, unlike dragonflies, antlions have well-developed, clubbed antennae roughly as long as the combined length of the head and thorax. Another distinguishing feature is the shape of the hypostigmal cell located in the distal part of the wing; it is elongated and narrow [7]. Both pairs of wings are similar in shape and size, with dense venation. Many species have distinct spots on their wings. Their abdomen is long and slender.
As noted earlier, all Myrmeleontidae, including antlions, undergo complete metamorphosis with a distinct pupal stage. Remarkably, all larvae in this family are predatory. They possess robust, compact bodies with flat, heavily sclerotized heads and exceptionally large mandibles. Most larvae inhabit sand or loose soil. Because they are not territorial, many individuals can coexist within a small area. Adults, or imagines, are mainly crepuscular and are relatively weak fliers compared with dragonflies. They feed primarily on insects and occasionally on plant material. Females deposit their eggs in sand, and in temperate regions such as Europe it is the larvae that survive the winter.
The family contains over 2,000 species found in dry habitats worldwide, with highest diversity in arid and semi-arid regions of Asia, Africa, and Australia. In Europe, they are more common in the southern parts. In Poland, eight species have been recorded:
- Myrmeleon bore
- Myrmeleon formicarius
- Myrmeleon inconspicuus
- Acanthaclisis occitanica
- Dendroleon pantherinus
- Euroleon nostras
- Creoleon plumbeus
- Distoleon tetragrammicus
In Poland, the most commonly observed species are Myrmeleon formicarius and Euroleon nostras. In my own backyard, particularly in the sandy patches along the garden fence, I discovered a large aggregation of the latter. The remainder of this article will focus on my observations of this species.
Euroleon nostras
Euroleon nostras is a thermophilic species of antlion, first described in 1785 as Formicaleo nostras [8]. It occurs across nearly all of Europe, including Poland, and although not especially common, it may be locally abundant. Its preferred habitats include forest edges, inland sand dunes, and sandy trails. Adult individuals can reach a body length of up to 30 mm (1.18 inches), with a wingspan extending to as much as 70 mm (2.75 inches).
The presence of larvae can be easily identified by the conical pit traps they build in sand (Photo 1). The larva waits at the bottom with its mandibles open, ready to seize any prey that accidentally falls into the trap.
This insect is not a protected by law (unlike some other antlion species, such as Myrmeleon inconspicuus), so it can be carefully collected from the wild for observation under controlled conditions. That said, it’s important to handle it responsibly. There is never a good reason to harm any living creature unnecessarily, including insects.
Larvae can be observed from as early as June. They are easily collected by gently sifting the sand at the bottom of a pit. When disturbed, the larva often becomes motionless as a defense mechanism, making it easier to transfer onto a piece of paper or into a container for transport to a lab or classroom.
The larva has a distinctive appearance: thick-bodied, about 12 mm (0.47 inches) long, with grayish-brown coloration that provides effective camouflage (Photo 2).
The larva’s most distinctive feature is its disproportionately large mandibles. Its body is covered with chitinous hairs and small protuberances. The eyes are tiny and play only a minor sensory role, as the larva relies primarily on touch and vibrations to perceive its surroundings.
The legs are arranged in a way that facilitates efficient movement through loose sand. It moves by pushing backward, a strategy that allows it to easily slip between sand particles and dig pit traps.
Larvae live individually in conical sand pits where they wait for prey. Only the tips of their mandibles are visible above the sand. Euroleon nostras primarily feeds on ants, but will also consume other insects or arachnids that fall into the trap. Cases of cannibalism have also been observed, with larvae preying on adult females of their own species while they lay eggs.
Creating a small enclosure for an antlion is straightforward. I used a plastic box measuring 13 × 18 × 6 cm (about 5.1 × 7.1 × 2.4 inches) filled with a few centimeters (at least 1–2 inches) of dry, clean sand. The collected larva was placed on the surface (Photo 4A). A lid was unnecessary, since the insect cannot escape from such a container. In my experience, antlions do not require any special environmental conditions; room temperature and natural daylight are sufficient. They probably obtain most of their water from prey, but lightly moistening the sand once a week is advisable.
Upon placement, the larva often becomes motionless (Photo 4B), a typical defensive response. After a short while, it flips over (Photo 4C) and begins to burrow backward into the sand (Photo 4D), leaving characteristic marks on the surface (Photo 4E). Eventually, it starts to dig a trap in a circular motion, tossing sand outward from the center. Once the trap is complete, the larva hides at the bottom with only its mandibles exposed (Photo 4F).
To feed it, I dropped a single ant into the container, most often Formica fusca, although any local species worked as well. The ant usually fell into the trap while exploring, and in many cases the larva seized it immediately. If not, it would hurl sand at the prey to drive it deeper into the pit. I also tested other prey such as firebugs Pyrrhocoris apterus and isopods Porcellio scaber, which it handled with ease. When the larva was actively feeding, I supplied food about once per day.
Once captured, the prey's fate is sealed. The larva injects digestive enzymes and then sucks out the liquefied contents. This process takes a few minutes to an hour. The remaining exoskeleton is catapulted out of the pit, sometimes several inches away (Photo 5A–D). The launch happens so fast that even at 260 frames per second, video is blurred (Photo 5B).
In the wild, the larval stage may last for several years depending on food availability.
Interestingly, the digestive tract of antlion larvae ends in a blind sac, meaning they lack an anus. Their method of feeding, which involves external digestion and fluid ingestion, combined with the high efficiency of their digestive system, results in minimal waste. Any harmful byproducts accumulate in the body and are expelled during metamorphosis into the adult form [9].
The larva featured in this article was collected in May. In early August, it stopped feeding and maintaining its trap. Assuming it had died, I gently sifted the sand and discovered a small spherical cocoon coated with sand grains (Photo 6).
The larva had entered the pupal stage. I carefully reburied the cocoon under a thin layer of sand. I added a small dry twig to serve as a perch for the emerging adult to unfold its wings and covered the container with fine mesh to prevent escape. Then, I waited…
Patience paid off. After 27 days (33 since its last meal), the adult emerged through a small hole in the cocoon (Photo 7). In nature, adults can be seen until September.
While the larva may appear grotesque or even frightening, the adult antlion is elegant and beautiful in its own right (Photo 8).
One glance at its intricately veined wings confirms its identity as a lacewing. In this species, the wings also bear distinctive dark spots. Although it superficially resembles a dragonfly, its head with long, clubbed, curved antennae clearly identifies it as an antlion. Dragonflies, by contrast, have very small and almost invisible antennae (Photo 9).
After observation, the adult was released back into the environment where its larva had been found.
Adult antlions fly slowly and somewhat clumsily. They hunt smaller insects, particularly in the evening. Their lifespan is short, lasting only a few weeks, during which they reproduce and begin the next generation.
Personally, observing the antlion’s hunting strategy and developmental stages was a fascinating experience. This small and relatively unknown member of our native fauna surely deserves more attention from biology educators and nature enthusiasts alike.
Antlions in Culture
Although somewhat forgotten today, the antlions Myrmeleontidae have held a place in the culture and mythology of various civilizations across the world. References can be found in ancient Indian epics as well as medieval European bestiaries [10]. I would like to present a few examples from literature that are particularly close to my heart.
One charming depiction of the antlion appears in a children’s book by Finnish author Tove Jansson. Although written for young readers, the story offers plenty of delight and insight for adults as well. I am referring to Tales from Moominvalley, a work that can be seen both as a novel and as a collection of tales. In the second chapter, Moomintroll and Snufkin decide to take revenge on the Antlion for bothering Moominmamma. The author describes the insect’s predatory method with surprising biological accuracy, simply scaled up for dramatic effect, while also attributing some fantastical traits to the creature, such as a mane reminiscent of a lion, perhaps inspired by its name. Ultimately, the mischievous Antlion is thrown into a magical hat and transformed into “the world's smallest hedgehog” [11].
The antlion also makes an appearance in one of the most famous works by Samuel Langhorne Clemens, better known as Mark Twain. In Chapter 8 of The Adventures of Tom Sawyer, the title character addresses the antlion in a kind of incantation, using it in a superstitious ritual. In the 1925 Polish translation by Jan Biliński, the insect was mistakenly rendered as a “forest beetle,” yet Twain’s description of the sand pits leaves no doubt as to its true identity. In American English, antlion larvae are often called doodlebugs because of the tracks they leave in the sand (Photo 10). That is the exact term Twain uses in the original text. The translator likely confused it with a bark beetle such as Ips typographus, a true beetle (Coleoptera) that also creates intricate patterns, but under tree bark rather than in sand.
Finally, even legendary science fiction writer Arthur C. Clarke (author of the Space Odyssey series, Rendezvous with Rama, Childhood’s End, and many other works) referenced the hunting behavior of antlions in his 1961 novel A Fall of Moondust.
Refereces:
- [1] Krebs Ch. J., Ekologia. Eksperymentalna analiza rozmieszczenia i liczebności, Wydawnictwo Naukowe PWN, Warszawa, 1997 back
- [2] Weiner J., Życie i ewolucja biosfery, Wydawnictwo Naukowe PWN, Warszawa, 2003 back
- [3] Aspöck U., Phylogeny of the Neuropterida (Insecta: Holometabola), Zoologica Scripta, 2002, 31 (1), pp. 51-55 back
- [4] Aspöck et al., Cladistic analysis of Neuroptera and their systematic position within Neuropterida (Insecta: Holometabola: Neuropterida: Neuroptera), Systematic Entomology, 2001, 26, pp. 73-86 back
- [5] Poinar G. O., Stange L. A., A new antlion from Dominican amber (Neuroptera: Myrmeleontidae), Experientia, 1996, 52, pp. 383-386 back
- [6] Bogdanowicz W., Chudzicka E., Pilipiuk I., Skibińska E. (red.), Fauna Polski – charakterystyka i wykaz gatunków, tom II, Muzeum i Instytut Zoologii PAN, Warszawa, 2007, pp. 289-290 back
- [7] Myrmeleontidae, archivised: https://web.archive.org/web/20100728044530/http://www.entomology.umn.edu/museum/links/coursefiles/JPEG%20images/Neuroptera%20web%20jpeg/Myrmeleontidae.jpg [11.12.2022] back
- [8] Formicaleo nostras, online: http://www.animalbase.uni-goettingen.de/zooweb/servlet/AnimalBase/home/speciestaxon?id=18769 [01.12.2022] back
- [9] Arnett R. H., Jr., American Insects: A handbook of the insects of America north of Mexico, Van Nostrand Reinhold Co., Nowy Jork, 1985 back
- [10] Swanson M., The Gold-Digging "Ant-Lions" of India, online: https://www.antlionpit.com/golddigging.html [dostęp: 01.12.2022] back
- [11] Jansson T., Muminki, księga pierwsza Wydawnictwo „Nasza Księgarnia”, Warszawa, 2012, pp. 82-186 back
- [12] Twain M., Przygody Tomka Sawyera, Wydawnictwo Polskie, Lwów-Poznań, 1925 back
All photographs and illustrations were created by the author.
Marek Ples