How insects sometimes excrete ammonia as adults?

Some adult insects, although they usually excrete uric acid (making them uricotelic), can sometimes excrete ammonia directly—especially when they eat a protein-rich diet.

Because ammonia is highly toxic, this can only happen when insects have plenty of water to flush it out or when they need to get rid of waste quickly. Below is an easy breakdown of when and how adult insects excrete ammonia:

1. Blood-feeding insects

Example: Adult female mosquitoes

• High protein intake: After feeding on a protein-rich blood meal, mosquitoes generate a large amount of ammonia as a result of protein breakdown.
• Detoxification and excretion: Some of this ammonia is converted into less harmful compounds like glutamine or proline, while the rest is directly excreted through feces.

2. Terrestrial insects with bacterial symbionts

Examples: Cockroaches and termites

• Uric acid recycling: These insects store uric acid in their fat bodies. When they lack nitrogen in their diet, symbiotic bacteria (like Blattabacterium in cockroaches) break down uric acid into ammonia.
• Amino acid production: The insect then uses this recycled ammonia to make essential amino acids.
• Excess ammonia removal: Any leftover ammonia that isn’t reused is excreted from the body.

3. Aquatic species and life stage changes

• Environmental factors: Some insects, like shield bugs, can switch from excreting uric acid to excreting urea and ammonia when they are in a moist environment or during diapause (a resting phase).
• Larval to adult differences: Insects such as dragonflies excrete ammonia as aquatic larvae but shift to uric acid when they become land-dwelling adults.
• This ability to excrete ammonia in certain situations is linked to their evolutionary history or dietary needs.

4. Physiological mechanisms

The main organs for excretion in insects are the Malpighian tubules and the hindgut, which help remove ammonia from the body.

• Transport proteins: Special proteins like Rhesus (Rh) glycoproteins and ammonia transporters (AMTs) move ammonia across cell membranes.
• Acid trapping: In some insects, the excretory fluid becomes acidic, changing ammonia (NH₃) into ammonium (NH₄+), which gets trapped and excreted safely.