Which order includes social insects that construct complex nests?

The order that includes social insects known for constructing complex nests is indeed Isoptera. This order primarily comprises termites, which are well-known for their highly organized social structures and the elaborate colonies they build, often featuring intricate tunnel systems and towering mounds.

Termites play crucial roles in their ecosystems, including the decomposition of wood and other plant materials, which contributes to nutrient cycling in the environment. Their ability to work together in large colonies to create large and complex nests is a defining characteristic of their social behavior. This cooperation distinguishes them from other insect orders, as many groups do not exhibit the same level of social organization or nest-building capability.

In contrast, the other choices do not pertain to social insects that engage in such construction. Siphonaptera refers to fleas, which are parasitic and do not build nests. Diptera includes flies, which lack a social structure or the propensity to build cooperative nests. Dermaptera, or earwigs, may live in aggregations but do not create the complex nest structures seen in Isoptera. Understanding the characteristics of these various orders helps clarify the unique traits that define social insects like termites within the Isoptera order.