Nymph (biology)

In insects with simple metamorphosis (hemimetabolism) and also in many other invertebrates, the immature stages or stages that, unlike larvae, are similar to adults, are called nymphs. those that differ due to the lack of maturity of the gonads (sexual organs that produce gametes), due to the smallness of the appendages that are found where the wings are in the adult - wing buds, in winged insects -, and in the size, smaller. They go through molts, called ecdysis, between each stage. The number of instars is usually fixed for each species. The nymphs of some species of Ephemeroptera can have up to 45 instars.

When the immature stages do not show wing buds, they are called neanids.

The term larva is reserved for the juvenile phases of groups in which there is complete metamorphosis, or holometabolism. The larvae are profoundly distinguished from the adults, with different internal and external anatomies and sometimes also feeding habits, etc., and go through the pupal stage before becoming adults.

Orders of insects with nymphs

The orders of insects with nymphs in their juvenile phases are:

Tick nymphs

At each stage of development (larva, nymph and adult), ticks must drink the blood of a vertebrate host at least once before they can move on to the next stage. During short-term sucking, male ticks do not feed on blood, but rather suck a small amount of tissue fluid. The larvae feed on the host for 2 to 5 days, after which they disappear, molt and become nymphs. In turn, the nymphs reattach to the vertebrate host for 2-7 days, then their metamorphosis occurs and they become adults.

The nymphal phase of tick development can be represented by 1-3 stages. Thus, ticks that are of a certain age are usually called protonymphs, deutonymphs and tritonymphs. Before the transition from one age to another, ticks fall into a dormant state for a while and then molt. All three ages of nymphs listed above are present in Carapace and Argas ticks. In sarcoptoids (feather mites, flour mites, hairy mites) only two obligatory instars (1 and 3) and one optional instar (2) are preserved; theranicoid mites also usually have only two nymphal instars.

The protonymph (nymph of the first age) is characterized by the "acquisition" of the fourth pair of legs, on which and around which are a small number of bristles. The protonymph also has a genital opening with a pair of genital tentacles and genital bristles. The lateral organs are lost. The deutonymph (nymph of the second age) is distinguished by the increased arming of the limbs with setae, their number increases and they are already present in all segments of the fourth pair of legs. In addition, a total of 2 pairs of genital tentacles and three pairs of genital setae are formed. In acaroid mites, the hypopus phase, or heteromorphic deutonymph, is also usually distinguished, which is formed in conditions unfavorable for development, lacks mouth organs and exists without feeding. The purpose of the existence of the hippopus is to ensure the survival of the species. The tritonymph (senior nymph) is characterized by the appearance of a third pair of genital tentacles and several additional setae. There is also an addition to the tactile armament of all the legs and integuments of the body.

Winged insect nymphs

Dragonfly nymphs

Dragonfly larvae are often called nymphs or naiads. In external morphology, they differ from adult dragonflies to a greater extent than the larvae of other groups of insects with incomplete metamorphosis, mainly in the structure of the respiratory system and mouth apparatus. This is due to their aquatic lifestyle, and not terrestrial, as in the sexually mature stage of development. The body of the larvae has a different shape. In representatives of some groups, it is very short and thick, completely different from the body of an adult dragonfly. In other groups, more elongated and slender, more similar to the body of an imago, but always thicker and shorter than it. The head of dragonfly larvae is large and wide and, with the exception of the mouthparts, is arranged in the same way as that of adults. A characteristic feature of the head structure of dragonfly larvae is the oral apparatus, which consists of an unpaired upper lip, paired upper jaws, paired lower jaws and an unpaired lower lip. Mask which is a unique organ of the dragonfly larvae. When capturing prey, it opens quickly and lunges forward, while the teeth at its front end pierce deeply into the victim. When the mask is folded, the prey is brought closer to the mouth and chewed calmly. At rest, the mask covers the head from below and (or) from the sides. A flat mask at rest covers the mouth of the larva only from below (its central plate is more or less flat, the side lobes lie together with it in the same plane), and the helmet-shaped mask simultaneously covers from above, in front and below, like a visor or shovel. This type is typical, for example, for representatives of the genera yugo and vigilante, which grabs prey with large movable teeth on its lateral lobes. The second type of mask is characteristic of slime-dwelling larvae, such as those of genera such as flatbellies and clubbelly. These larvae capture prey along with slime, and then the small particles are sifted through a kind of "sieve" formed by long central and lateral bristles on the mask. A characteristic feature of the limbs of the larvae is the structure of the trochanter: its muscles do not enter the base of the thigh, but are attached to a stretched membrane that supports the thigh. If you grab the larva by the leg, the muscles of the trochanter contract, causing a rupture of the membrane, and the thigh easily separates from the coxa. In the early stages of development, the larvae can regenerate the lost limb, but not in the later stages. For most of their lives, dragonfly larvae cannot breathe atmospheric air and use gills for breathing, located at the end of the body, which can be internal (rectal) or external (caudal). On the abdomen of the larvae of most damselfly dragonflies (Zygoptera) caudal tracheal gills develop, which may look like transparent leaf-shaped plates or oval capsule-shaped (vesicle-shaped) appendages. In dragonfly larvae (Anisoptera), the tracheal gills are located in a special chamber in the rectum (rectal gills), which periodically fills with water.