The growth rate of a spider is highly variable, depending on species-specific genetics and environmental conditions. The timeline for a spider to reach maturity can range from a few months to over a decade. Factors like the spider’s adult size, habitat temperature, and food supply consistency all contribute to the speed of its development.
The Mechanism of Spider Growth (Ecdysis)
Spiders cannot grow continuously because they are protected by a rigid external skeleton called a cuticle. To increase in size, the spider must periodically shed this hard outer layer in a process known as molting. Before a molt, the spider secretes a new, larger, soft cuticle beneath the old one while reabsorbing nutrients from the inner layer of the old shell.
The process begins when the spider increases the pressure of its hemolymph to crack the old exoskeleton, typically along the carapace (the part covering the head and thorax). The spider then wiggles out of the old skin, often hanging from a strand of silk during the event. The discarded shell, known as the exuviae, contains the remnants of the old outer layer, including the linings of the internal tracts.
Once free, the spider is described as callow, meaning its new exoskeleton is soft, pale, and vulnerable. During this phase, which can last from minutes in small species to hours in larger ones, the spider rapidly expands its body size by pumping fluid into the soft new skin before it hardens and darkens. Molting is a risky time, as the soft-bodied spider is susceptible to predators and environmental issues, which can cause the old skin to become stuck, leading to injury or death.
Developmental Stages and General Timelines
All spiders progress through three life stages: the egg, the spiderling, and the adult. Spiders begin their lives inside an egg sac, constructed from silk by the female, which can contain anywhere from a few to several hundred eggs. Depending on the temperature, the eggs may hatch in a few weeks, or in temperate regions, they may overwinter in the sac and hatch the following spring.
Upon emerging from the sac, the spiders are called spiderlings. They must undergo a series of molts to grow, with most species requiring between five to ten molts to reach sexual maturity. The time between molts shortens when the spider is young and lengthens as it ages; some species, known as Araneomorphs, stop molting once they reach adulthood.
The total time to reach maturity varies dramatically between species. Many common house spiders, such as wolf spiders and jumping spiders, are short-lived, maturing in a few months and generally living for only one to two years. For instance, one species of jumping spider reached adulthood in about 137 days, spanning eight spiderling stages. In contrast, mygalomorph spiders, which include tarantulas, are long-lived and require significantly more time to develop. Female tarantulas can continue to molt annually even after reaching sexual maturity and may live for 20 years or more.
Environmental Factors That Affect Growth Speed
The speed at which a spider progresses through its developmental stages is regulated by environmental factors. Temperature is a major influence on growth speed because spiders are ectotherms; their body temperature and metabolic rate are closely linked to the surrounding temperature. Generally, warmer conditions accelerate metabolic processes, leading to faster development and more frequent molting up to a certain point. However, temperatures that are too high can slow development or become lethal, causing eggs to fail to hatch or juveniles to experience reduced growth.
The availability and consistency of food also impact how quickly a spider grows and molts. A steady supply of abundant prey provides the necessary energy and nutrients to build a larger body size. Spiders with a high feeding rate survive to adulthood in greater numbers and grow more rapidly than those with a restricted diet. Conversely, spiders often stop feeding for several days before a molt as their body prepares to shed the old exoskeleton, which temporarily halts the growth cycle.
Finally, species variance dictates the maximum potential growth rate. Spiders that are genetically predisposed to be smaller, such as jumping spiders, naturally reach maturity more quickly than those with a large adult size, like tarantulas. The required number of molts and the time between each molt are species-specific traits that determine the overall duration of the growth period.