What do antennae do for insects

The site of the cut determines the outcome of the regeneration: distal cuts lead to a "correct" antenna regenerate, proximal cuts lead to complete failure of regeneration. Note that there is also a Drosophila gene called Antennapedia. Morphological similarity between walking legs and antennae concerns the structure of joints, musculature, innervation and most types of mechanoreceptors and contact chemoreceptors Staudacher et al.

Differences concern the number of functional segments five in legs, three in antennae , cuticle properties see below and sensory infrastructure e. The antenna has three functional segments: they are called scape, pedicel and flagellum, from base to tip. This is the same in all higher insects the Ectognatha; see Imms, In other words, true joints that are capable of active, muscle-driven movement occur only between head and scape HS-joint and between scape and pedicel SP-joint.

The HS-joint is moved by three muscles inside the head capsule so-called extrinsic muscles, because they are outside the antenna , the SP-joint is moved by two muscles inside the scape so-called intrinsic muscles, because they are located inside the antenna.

Several morphological, biomechanical and physiological properties of the stick insect antenna are beneficial for its function in tactually guided behaviour. Four of such adaptations are:. Since stick insects generally are nocturnal animals, their antennae are likely to be their main "look-ahead sense" rather than the eyes. Moreover, as many stick insect species are obligatory walkers, tactile exploration is likely to serve obstacle detection and orientation during terrestrial locomotion.

Thus, potentially, anything the antenna touches is located within reach of the front leg. As Fig. Owing to this match, the stick insect is able to adapt its locomotory behaviour to a touch event within the action distance of one length of a leg, and with a look-ahead time of up to one step cycle period.

Some of these descending interneurons have been characterized individually to quite some detail. For example, a set of three motion-sensitive descending interneurons encodes information about antennal movement velocity in a complementary manner: two of them respond by increases in spike rate, the third one responds by a decrease in spike rate Ache et al.

Because these movement-induced changes in spike rate occur with very short latency approx. Note that the length of the antennae does not match the length of the front legs in all stick insect species.

In some species, like Medauroidea extradentata Redtenbacher , the antennae are much shorter than the front legs, indicating that their antennae are not suited for tactile near-range searching because the feet of the front leg will nearly always lead the antennal tips.

In the case of M. Thus, in these animals the front legs appear to take on the function of tactile near-range searching.

Temporal coordination is revealed by the gait pattern of a straight walking stick insect in Fig. The pattern is the same for left and right limbs. In both cases, coordination is well-described by a rear-to-front wave travelling along the body axis indicated by grey arrows.

As if activated by such a wave, the middle legs follow the hind leg rhythm, the front legs follow the middle legs, and the antennae follow the front legs. Note that this pattern depends on walking conditions and behavioural context. Antennae and front legs are also coordinated spatially Fig. Both, temporal and spatial coordination support the hypothesis that the antenna actively explores the near-range space for objects which require the ipsilateral leg to adapt its movement.

Indeed, it has been shown that the likelihood of the antenna to detect an obstacle before the leg gets there, i. As mentioned above, all higher insects have only two true joints per antenna Imms, , meaning that only two joints are actively moved by muscles.

In stick insects, both of these joints are revolute joints hinge joints with a single, fixed rotation axis. Because of the fixed joint axes, a single joint angle accurately describes the movement of each joint they have a single Degree Of Freedom , DOF.

Therefore, the two DOF associated with the two revolute joints of a stick insect antenna, fully describe its posture. For example, if both joint axes were orthogonal to each other, and if the length of the scape was zero, the antennal joints would work like a universal joint or Cardan joint : the flagellum could point into any direction. Because the scape is short relative to the total length of the antenna, its length has virtually no effect on the action range of the antenna.

This is different than in other insect groups, for example crickets, locusts and cockroaches. Mujagic et al. Essentially, this is because the surface of the area that can be reached by the antennal tip decreases due to the out-of-reach zone , but the number of possible joint angle combinations stays the same.

Therefore, theoretically, an arrangement with out-of-reach zones has improved positioning accuracy. Since the order of the stick insects Phasmatodea is thought to have evolved as a primarily wingless group of insects Whiting et al. The finding that slanted, non-orthogonal joint axes are an autapomorphy of the Phasmatodea suggests that this insect order has evolved an antennal morphology that is efficient for tactile near-range sensing Mujagic et al.

Last but not least, there are particular biomechanical features that support the sensory function of the antenna. In particular, this concerns the function of the delicate, long and thin flagellum that carries thousands of sensory hairs. In Carausius morosus , the flagellum is about times as long as its diameter at the base.

If this structure was totally stiff, it would break very easily. In the other extreme, if it was too flexible, it would be very inappropriate for spatial sampling, simply because its shape would change all the time.

As a consequence, much of the sensory resources would have to go into monitoring the own curvature, at least if contact locations in space were to be encoded. For example, the flagellum frequently bends very much as the stick insect samples an obstacle during climbing. The structure of the cuticle, i.

Owing to the different material properties of the inner and outer cuticle layers, the water-rich inner endocuticle supposedly acts like a damping system that prevents oscillations that would be caused by the stiff material alone. As a result, a bent antenna can snap back into its resting posture without over-shoot, a sign of over-critical damping.

The basic form of antenna is filiform. In this type there are many segments that are more or less equal in size. The length and number of joints varies much between them. This basic structure is modified in a wide variety of ways. This means that a number of different types may be recognised. The main ones are as follows They use their antennae to touch and smell the world around them. Adult insects and most immatures have six legs that are attached to the middle section of the body, the thorax.

Insects are the only arthropods that have wings, and the wings are always attached to the thorax, like the legs. All insects lay eggs. There are two ways that insects grow: complete or incomplete metamorphosis.

Insects that have complete metamorphosis have babies that look very different from the adults and often eat very different foods than adults.

Butterflies, beetles, and true flies are some of the groups that have complete metamorphosis. The babies are called larvae. Caterpillars and maggots are examples of insect larvae. Larvae often have soft exoskeletons that stretch so they can grow fast, and they go through a resting stage called a pupa before emerging as an adult.