Question

A dorsal horn is present on the ………… of the mulberry silk worm (caterpillar)
A) Head
B) 8th abdominal segment
C) 5th abdominal segment
D) 2nd thoracic segment

Answer 1

Hint: Caterpillar has a more or less cylindrical body composed of three main parts, namely head, thorax and abdomen. The abdomen consists of 10 visible segments. Most caterpillars have a single pair of prolegs on segments 3 to 6 and on the 10th segment.

Complete answer:
Caterpillars are the larval stage of butterflies and moths. They are voracious eaters, usually feeding on fresh fruits and vegetables. Due to this reason, caterpillars are considered as main agricultural pests, though some species actually help control overgrowth by feeding on pest plants.

Caterpillars come in many colors, shapes and sizes. Some caterpillars are quite hairy, while others are smooth. Despite differences between species, all caterpillars share certain morphological features. In caterpillar, head is a single unit, but actually it is composed of six fused segments that create a tough, hardened (sclerotized) head capsule. The head bears the feeding and sensory appendages. The horn is a dorsal projection present on some caterpillars. It may help camouflage the larva. It is also used to frighten away predators.

Head includes six eyes called (stemmata), mouth parts, small antennae and the spinnerets from which caterpillars produce milk. Antennae are present on either side of the labrum but are small and relatively inconspicuous. The labrum is like an upper lip. It is used to hold food in place while the mandibles do chew.

The thorax is the second section of the caterpillar body. It consists of three segments. The thorax contains three pairs of true legs with hooks and a dorsal plate called the prothoracic shield. The prothoracic shield is located on the first segment. The color pattern of this shield is valuable for identifying different species of caterpillars.

The third section of the caterpillar body is the abdomen. It is 10 segments long and includes the prolegs (false legs), most of the spiracles (breathing holes used for respiration) and the anus. The abdomen contains five pairs of unjointed prolegs or pseudo legs. One pair each in 3rd to 6th segments and anal leg on the 10th segment. It also contains a short dorsal horn on the 8th segment.

So, here the correct answer is option (B) 8th abdominal segment.

Note:A silkworm’s preferred food are white mulberry leaves, though they may eat other mulberry species. Domestic silk moths are closely dependent on humans for reproduction. Wild silk moths are different from their domestic cousins as they have not been selectively bred, thus they are not commercially viable in the production of silk.