THE ANIMAL FILES

Red imported fire ant

Solenopsis invicta

Workers differ in proportions, not just in overall size.

Red imported fire ant workers vary in size, and their head and antennal proportions do not change in perfect lockstep. The differences become clearer late in larval development, while pupae already show the outline of the adult body.[1]

Follow the evidence ↓
Red imported fire ant
Image: April Nobile · Commons · CC BY 4.0
Development
Egg, larva, pupa and adult[1]
Worker sizes
Small and large workers occur[1]
Pupal posture
Legs and antennae lie close to the body[1]

Small larvae can conceal later differences

Larvae pass through four described instars. Small-worker and large-worker larvae are difficult to distinguish before the final instar, when size differences become clearer. Comparing early larvae alone therefore provides less information about their eventual adult size than a later developmental sample.[1]

The pupa exposes the coming body plan

Pupae resemble adult ants but hold the legs and antennae against the body. They begin pale and darken as maturation approaches. Those changes accompany development inside a stationary stage; they do not represent a pale adult simply putting on colour after beginning its normal working life.[1]

Scaling is not identical in every part

When workers of different sizes are compared, head shape changes and antennae are proportionally shorter in larger bodies. Relative measurements reveal this difference better than total length alone. This comparison concerns different adult workers; it does not mean that one adult continuously grows into a larger worker after emergence.[1]

A COMMON MIX-UP

Is a large worker simply a small worker enlarged uniformly?

No. Body parts change in relative proportions across worker sizes. Head shape and antennal length provide measurable examples of non-uniform scaling.[1]

TRY A LITTLE REASONING

Why divide antenna length by body length when comparing workers?

Reveal the explanation

The ratio separates relative proportion from overall size. A larger worker can have longer antennae in absolute terms while still having shorter antennae relative to its body length.[1]

Sources & editorial notes

Adapted and translated from the cited Wikipedia revisions, with source-linked reasoning. Image credit and licence are listed separately above.

Adapted and translated from Wikipedia contributors; exact revisions are linked below. CC BY-SA 4.0

  1. Wikipedia contributors — Red imported fire ant (fixed revision; adapted and translated)
  2. NCBI Taxonomy — Solenopsis invicta (identity and classification)

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