Earwig larvae, more precisely called nymphs, are miniature versions of the adults that hatch from eggs in underground nests, typically in early spring. They pass through four or five molts before reaching maturity, growing their signature forceps a little more with each stage. What makes earwig nymphs genuinely unusual among insects is the level of parental care they receive: their mothers guard, groom, and even feed them mouth-to-mouth, a behavior rare enough in the insect world to have attracted decades of research.
What Earwig Nymphs Look Like
When earwig nymphs first emerge from their eggs, they are pale, soft-bodied, and only a few millimeters long. They resemble adult earwigs in basic shape but lack fully developed wings or the hardened, curved forceps (cerci) that make adults so recognizable. The forceps at this stage are short, straight, and relatively soft. With each successive molt, nymphs darken in color, grow larger, and their forceps lengthen and begin to curve. In males, the forceps eventually become noticeably asymmetrical. Research tracking forceps growth through four successive instars found that compensatory growth mechanisms keep asymmetry in check during the middle molts, so the relative asymmetry actually decreases even as the forceps get longer and more curved.1PubMed. The Ontogeny of Asymmetry in Earwig Forceps
In at least one basal earwig species, the transition from nymph to adult involves a startling step: the final-instar larva eats its own thread-like cerci, leaving only the base segments behind, before a pair of adult forceps appears during the final molt.2Arthropod Systematics & Phylogeny. Reproductive biology and postembryonic development in the basal earwig Diplatys flavicollis (Shiraki) This self-consumption of the juvenile cerci is not seen in all earwig families, but it highlights how dramatically the body plan can change during the last developmental transition.
Maternal Care That Rivals Some Vertebrates
The most striking thing about earwig larvae is the care their mothers invest in them. Female European earwigs dig a small burrow in soil or leaf litter during autumn, lay a clutch of eggs, and then stay with those eggs through the winter. During this brooding period, the mother regularly licks the eggs to prevent fungal growth and rearranges them in the nest. Once the nymphs hatch, she does not simply leave. She stays for weeks, continuing to guard and provision them.
Mothers actually regurgitate food for their nymphs. Researchers demonstrated this by feeding mothers food colored with one dye and offering the nymphs food colored with a different dye, then checking what color appeared in the nymphs’ guts. The result confirmed significant food transfer from mother to offspring, meaning nymphs were not just eating on their own but receiving pre-processed meals directly from their mother’s mouth.3Ethology. Maternal Food Regurgitation to Nymphs in Earwigs (Forficula auricularia) This mouth-to-mouth feeding is the kind of behavior you might associate with birds or mammals, not insects.
The mother’s presence is not optional for nymph survival. A field experiment that removed tending mothers from their nests found substantially fewer occupied burrows and fewer surviving larvae compared to nests where mothers remained. The researchers could not entirely separate whether the nymphs died without maternal protection or simply dispersed from the unguarded nest, but either way, the family unit fell apart without her.4Ecological Entomology. Maternal attendance and the maintenance of family groups in common earwigs (Forficula auricularia): a field experiment
Interestingly, earwig mothers do not appear to recognize their own offspring as individuals. Research on the striped earwig showed that females could not distinguish their own nymphs from unrelated ones. Instead, they recognized their own nest by chemical cues they had deposited on the burrow walls.5Ethology. Maternal Behaviour and Nest Recognition in the Subsocial Earwig Labidura riparia Pallas (Dermaptera: Labiduridae) This means that if foreign nymphs wander into a mother’s nest, she will likely care for them as if they were her own. The field study on European earwigs similarly noted that adoption and clutch-joining affect the social structure of the species, suggesting that mixed broods are a natural occurrence, not a laboratory oddity.6Ecological Entomology. Maternal attendance and the maintenance of family groups in common earwigs (Forficula auricularia): a field experiment
Siblicide and Cannibalism Among Nymphs
For all the tender care earwig mothers provide, life inside the nest is not peaceful among siblings. Earwig nymphs kill and eat each other, and the pattern is not random. Experiments grouping nymphs of mixed relatedness found that unrelated individuals were killed earlier and cannibalized more often than related ones. The survival patterns matched predictions from evolutionary theory about when harming relatives is “worth it” from a gene’s-eye perspective: nymphs recognized kin and were more restrained around them.7Behavioral Ecology. Kin-selected siblicide and cannibalism in the European earwig
Body size plays into this dynamic. When researchers set up groups of three nymphs and varied both kinship and weight differences, they found that size asymmetry amplified the killing, but primarily among unrelated nymphs. Related nymphs with the same weight differences were less likely to kill each other, suggesting that kinship acts as a brake on aggression even when one nymph is substantially bigger than another.8Animal Behaviour. Influence of weight asymmetry and kinship on siblicidal and cannibalistic behaviour in earwigs Given that foreign nymphs can join a brood (as noted in the section on maternal care), unrelated newcomers face real danger from resident siblings.
The mother’s own condition can influence how aggressively nymphs behave. When researchers manipulated the apparent condition of mothers, they found that nymph survival was affected by the interaction between the mother’s state and when the brood hatched. In early-hatching broods, nymphs whose mothers appeared to be in poor condition actually survived at higher rates, while the pattern reversed for late-hatching broods.9PLOS ONE. Cues of Maternal Condition Influence Offspring Selfishness The implication is that nymphs pick up on cues about their mother’s health and adjust their behavior accordingly, possibly competing more fiercely when future provisioning looks uncertain.
How Larvae Defend Themselves
Earwig nymphs are small, soft, and slow compared to many predators, but they are not defenseless. Like adults, nymphs have glands that produce chemical secretions, though the specific glands differ between life stages. In adult earwigs, defensive chemicals come from glands at the tips of the abdomen. In nymphs, the secretions originate from a different set of abdominal glands called pygidial glands.
Analysis of these larval secretions identified a cocktail of benzoquinones and hydrocarbons. When tested against common predators, the secretion discouraged foraging by ants but had no deterrent effect on spiders. Nymphs released the secretion specifically in response to ant attacks, suggesting a targeted rather than general defense. The researchers proposed that earwigs switch gland systems during development, using different chemical arsenals at different life stages.10PubMed. The chemical defense in larvae of the earwig Forficula auricularia For nymphs living underground in ant-rich environments, an anti-ant chemical weapon is a practical adaptation, even if it leaves them vulnerable to other predators.
What Controls How Fast Nymphs Grow and Whether They Survive
The interval between molts and the likelihood of surviving to the next one depend heavily on two factors: body weight and temperature. Laboratory experiments on European earwig nymphs found that heavier nymphs molted sooner than lighter ones, and nymphs kept at 24°C molted earlier than those at 20°C. But the higher temperature came at a cost: nymphs maintained at 24°C also died faster when food was scarce, and lighter nymphs were especially vulnerable.11Journal of Insect Physiology. Effects of temperature, fungal infection and weight on intermoult duration and survival of starving earwig larvae In effect, warmth speeds up the developmental clock but burns through energy reserves more quickly, a tradeoff that becomes critical during the unpredictable conditions of spring.
Fungal pathogens add another layer of risk. High concentrations of pathogenic fungi killed nymphs faster, though exposure did not change the timing of their next molt. This means a nymph that survives infection does not delay its development, but the infection makes survival to that next molt less likely.12Journal of Insect Physiology. Effects of temperature, fungal infection and weight on intermoult duration and survival of starving earwig larvae
Winter is the most dangerous season for earwig populations overall. Studies in orchards have found that between 60 and 90 percent of adult females do not survive the winter months, with parasitism contributing up to about 20 percent of deaths depending on species, year, and location. Agricultural practices matter too: soil tillage in winter can cut the number of nymphs that emerge the following spring by roughly half, because it physically destroys the shallow nesting burrows where females are brooding their eggs.13Journal of Applied Entomology. Natural and human causes of earwig mortality during winter: temperature, parasitoids and soil tillage
Where Nymphs Live and How They Use Their Habitat
Earwig nymphs do not always stay in the nest burrow. After the period of maternal care ends, usually a few weeks after hatching, nymphs disperse and begin foraging on their own. In forests, surveys have found that the vertical distribution of earwigs through the canopy differs by developmental stage: nymphs and adults do not always occupy the same heights or the same tree species.14Entomological Science. Vertical distribution of earwigs (Dermaptera: Forficulidae) in a temperate lowland forest, based on sampling with a mobile aerial lift platform This stage-specific stratification probably reflects differences in body size, microclimate needs, and diet between nymphs and adults.
In gardens and agricultural settings, earwig nymphs emerge in spring and can be found under stones, bark, mulch, flower pots, and in any tight, damp crevice. They are nocturnal feeders, like the adults, and are omnivores from the start. Nymphs eat soft plant material, aphids, mites, and decaying organic matter. The balance between plant feeding and predation depends on what is available, and it changes through the season as both the nymphs grow and the prey community shifts.
Friend or Foe in the Garden
The question of whether earwigs (including their nymphs) are pests or beneficial predators does not have a clean answer. It depends entirely on the crop. A review of European earwig biology across fruit-growing systems concluded that earwigs generally play a net positive role in apple and pear orchards, where they consume pest insects and rarely damage the fruit. In stone fruit orchards (cherries, peaches, plums), the situation reverses: soft fruit is vulnerable to earwig feeding, and the damage outweighs the pest control benefit.15Journal of Integrated Pest Management. Biology and Management of European Earwig in Orchards and Vineyards
Citrus presents an intermediate case. A study in a Mediterranean organic citrus orchard found earwigs acting as both friend and foe simultaneously: they reduced aphid infestations but also damaged flowers. However, the damage to flowers did not ultimately reduce fruit yield because the trees naturally shed excess flowers and fruitlets on their own, compensating for the earwig feeding.16Biological Control. Friend or foe? The role of earwigs in a Mediterranean organic citrus orchard For home gardeners, the practical takeaway is that earwig nymphs appearing among your plants in spring are likely doing more pest control than plant damage, unless you are growing soft fruit or tender seedlings.
Gut Microbes and Their Surprising Role
Like many insects, earwigs harbor communities of gut bacteria, and researchers have wondered whether these microbes play a role in maternal care behaviors. When researchers disrupted the gut microbiome of earwig mothers using a broad-spectrum antibiotic, the treatment clearly altered the mothers’ microbial communities and increased their feces production. It also resulted in lighter eggs and lighter nymphs. But the antibiotic did not change the mothers’ caregiving behavior, either before or after hatching.17PubMed Central. Alteration of gut microbiota with a broad-spectrum antibiotic does not impair maternal care in the European earwig The finding that nymphs were lighter is worth noting: it suggests that the mother’s gut microbiome affects the resources she transfers to her eggs, which in turn affects how well-equipped nymphs are at the start of life. But the drive to care for offspring appears to be independent of microbial signaling, at least based on this work.
The Outliers That Give Birth to Live Young
Most earwigs lay eggs and brood them in a nest, but a few lineages have evolved something far more unusual. Hemimerus, a genus of earwigs that live on the skin of giant rats in sub-Saharan Africa, are viviparous: they give birth to live nymphs that develop inside the mother’s body. Research into this system uncovered an organ with no known parallel in the insect world. The developing embryo grows a “cephalic vesicle” on its head that integrates both maternal ovarian tissue and embryonic tissue into a structure that functions as an intraovarian analogue of a placenta. The contractions of muscle cells around the embryo’s blood vessel appear to transport nutrients from the mother’s follicular cells directly into the embryo’s circulatory system.18PLOS ONE. Unusual morphological adaptations and processes associated with viviparity in an epizoic dermapteran
Hemimerus nymphs emerge fully formed and already adapted to their unusual lifestyle, clinging to rat fur. They never pass through a free-living soil stage. This is about as far from the typical earwig larval experience as you can get while still being in the same order of insects, and it shows that earwig reproduction is more diverse than the common garden species would suggest. The discovery of a placenta-like organ in an insect lineage underscores how convergent evolution can produce functionally similar solutions across wildly different animal groups when the selective pressure, in this case the need to nourish embryos internally, is strong enough.