The duration of maternal care for baby spiders, known as spiderlings, varies widely, ranging from immediate independence to periods lasting a year or more. This variability is defined by whether the species is solitary or exhibits subsocial behavior. Solitary species, which make up the majority, typically provide little direct care beyond protecting the egg sac. Subsocial species, however, demonstrate a much longer commitment to their offspring.
Variability in Maternal Care Duration
The time spiderlings spend under maternal supervision varies significantly across species, often spanning a range from a few days to many months. In many web-building spiders, such as common orb weavers, the young disperse almost immediately after emerging from the egg sac and completing their first molt. This rapid separation minimizes competition for resources and avoids the risk of cannibalism.
Hunting spiders and those with complex social behaviors show prolonged care. Female wolf spiders carry their egg sac attached to their spinnerets until the spiderlings hatch. Once emerged, the spiderlings crawl onto the mother’s back, where she transports them for a period lasting from a few days to several weeks. Black widow spiderlings typically remain in a dense congregation within the mother’s web for about one to two weeks before dispersing.
The longest periods of maternal association occur in subsocial and social spider species. In these groups, the mother and young may share a communal web, with care extending for several instars, or molts. For some social species, the young remain with the parent for three to five weeks. In highly social species, the association can endure for up to a year or until the young reach near-adulthood. The duration of this care is influenced by environmental factors, such as prey availability, which determines the pressure to separate and find new territory.
Early Developmental Stages Under Parental Supervision
Before achieving independence, several developmental milestones occur under the mother’s protection. The initial stage involves the mother guarding the egg sac, either carrying it (as seen in wolf spiders) or securing it to a retreat. Inside this protective silk casing, the eggs hatch and the spiderlings undergo their first molt, transitioning into the first instar, which is the first true spider form.
Upon emerging from the egg sac, spiderlings remain vulnerable and rely on the mother for defense. Nursery web spiders construct a silk tent, or nursery, where the spiderlings are protected for about two weeks while the mother stands guard nearby. Some tarantula species guard the young in their burrow for the first few molts.
Direct feeding is uncommon, but some mothers support their young’s early survival. Certain tarantulas may kill prey and leave it near the young, or a mother may regurgitate liquid food for her offspring. In the most extreme examples of maternal investment, the mother may die, allowing the spiderlings to feed on her body. This self-sacrifice, known as matriphagy, provides a rich nutrient source for the newly hatched young.
Mechanisms of Spiderling Dispersal
The end of maternal care is marked by the separation of spiderlings from the mother and their natal territory. This dispersal reduces local competition and avoids inbreeding. For those that remain with the mother for only a short time, the most common method is simple walking or running away from the nest site.
A more well-known mechanism is aerial dispersal, commonly called ballooning. To initiate this process, a spiderling climbs to a high point, such as a fence post or blade of grass, and assumes a “tiptoe” stance with its abdomen pointed upward. The spiderling then releases fine strands of silk, known as gossamer, from its spinnerets into the air.
These silk threads catch air currents, and the spiderling is lifted and carried away, sometimes traveling vast distances across land and water. Studies also suggest that spiderlings use the Earth’s electrostatic field to achieve lift, allowing them to become airborne even when there is little wind. This mechanism allows for the wide distribution of species and is the primary way many spiderlings, including wolf spiders and orb weavers, establish new, independent territories.