In insects and spiders, which structures function as the main excretory organs responsible for removing nitrogenous wastes from the body?

Introduction / Context:
Excretion is the biological process by which animals remove nitrogenous waste and maintain internal chemical balance. Different animal groups use different excretory organs, and questions about these organs frequently appear in general science and biology examinations. Insects and many arachnids, such as spiders, use a special type of excretory organ that is distinct from the kidneys found in vertebrates. Identifying this organ is the central goal of this question.

Given Data / Assumptions:

• The animals in focus are insects and spiders.
• We are asked to identify their main excretory organs.
• Options list several named glands and structures found in different invertebrates.
• We assume standard zoology terminology used in school and competitive exam curricula.

Concept / Approach:
Insects and many arachnids possess Malpighian tubules as their principal excretory organs. These fine, blind ended tubules extend from the junction of the midgut and hindgut into the body cavity. They absorb nitrogenous wastes like uric acid from the hemolymph and transfer these wastes into the gut for elimination with feces. Other organs named in the options, such as coxal glands, antennal glands, and green glands, belong to different arthropod groups such as crustaceans. Therefore, the correct approach is to recall which excretory organ is characteristic of insects and spiders and match it with the options given.

Step-by-Step Solution:
Step 1: Recall that insects and many spiders belong to the phylum Arthropoda but differ from crustaceans in their excretory structures. Step 2: Remember that in insects and many arachnids, excretion is mainly carried out by Malpighian tubules. Step 3: Note that Malpighian tubules are slender, tubular structures that open into the alimentary canal and remove waste from the hemolymph. Step 4: Check the options and identify Malpighian tubules as option A. Step 5: Confirm that other listed glands are associated with certain crustaceans or other groups and are not the primary excretory organs of insects and spiders.

Verification / Alternative check:
A quick verification method is to link each organ with the typical organism in which it occurs. Antennal glands and green glands are characteristic of aquatic crustaceans such as prawns and crayfish. Coxal glands can be present in some arachnids, but Malpighian tubules are widely recognized as the main excretory organs in insects and many spiders. Maxillary glands are not described as the principal excretory organs for these groups in standard zoology texts. Hence, Malpighian tubules clearly stand out as the correct answer.

Why Other Options Are Wrong:
Option B: Maxillary glands are not the primary excretory organs described for insects and spiders in standard classifications. Option C: Coxal glands can occur in some arthropods, but Malpighian tubules are recognized as the main excretory organs in insects and many spiders. Option D: Antennal glands are characteristic of crustaceans such as prawns, not of insects and spiders. Option E: Green glands are also associated with crustaceans and are not described as the main excretory organs in insects and spiders.

Common Pitfalls:
Learners often confuse the different excretory organs of arthropods because many names sound similar or are associated with appendages such as antennae or maxillae. Another common error is to assume that all arthropods use the same excretory structure. In reality, insects and many arachnids rely mainly on Malpighian tubules, while crustaceans typically use antennal or green glands. Remembering one or two representative examples from each group can prevent this confusion during exams.

Final Answer:
The main excretory organs found in insects and many spiders are Malpighian tubules, which remove nitrogenous wastes from the hemolymph and pass them into the gut for elimination.