How long do flea cocoons live for?

Summary

Within cocoons, flea larvae develop into adults in 7-19 days. However, fully mature fleas can stay inside their cocoons for up to 5 months. Flea larvae create cocoons in 6.7 hours. They begin pupating 17.8 hours later. The first molt into pupae is completed 1.5 to 4 days after the cocoon is formed. The pupal stage lasts 6-7 days before the fleas complete their second molt into mature adults.

Details

Flea larvae usually pupate within cocoons. Inside the silk structure, they transition through three distinct stages: U-shaped larvae (prepupae), true exarate pupa, and pre-emerged (pharate) adult. They molt between each stage. There’s a larval-pupal molt, and a pupal-imaginal molt.

How Long it Takes Larvae to Spin Cocoons

Mature flea larvae shed their guts to prepare for pupation. Afterwards, they remain inactive for 11 hours. Once this brief quiescent period ends, they begin spinning a cocoon. The cocoon gets finished in 6.7 hours. Then movement ceases again.

How Long it Takes Fleas to Pupate

Within its cocoon, the immature flea develops into an adult over the course of 7-19 days. Males require 14-20% more time to mature than females. As temperature decreases, development time increases. At 60°F (15.5°C), prepupae become adults in 26.8 days (female) and 32.1 days (male). At 80°F (26.7°C), the mean number of days is 8 (female) and 10 (male).

Males
Females

Fig 1 Days (y-axis) it takes for cocooned larvae to become mature adults (x-axis).

Larval-Pupal Molt

Molt Process

Once the cocoon is formed, fleas begin pupating in around 17.8 hours. As a larva transitions into a pupa, body tissues are broken down and reorganized. Fluid in the last three body segments gets absorbed 6-12 hours before molting. The segments then collapse, and within 3-8 hours a pupa emerges from the old larval cuticle.

Males
Females

Fig 2 Days (y-axis) it takes for cocooned larvae to become pupae (x-axis).

Molt Duration

Females reach the pupal stage 12 hours earlier than males. At 80.6°F (26.7°C), female and male larvae become pupae in 31.5 and 43.6 hours, respectively. However, in some studies, the first molt took slightly longer (see Fig 2).

Pupal-Imago Molt

Molt Process

Shortly after shedding the larval cuticle, the pupa’s body gradually shortens and widens. It remains white for 5-9 days. Then it changes to yellow color for 2-3 days. Finally, it becomes brown. The flea’s combs and bristles turn black a day or two into the brown stage. These color changes occur on the underlying adult cuticle. The pupal cuticle remains colorless. 2-24 hours before molting, the legs break away from their close position on the abdomen.

Males
Females

Fig 3 Days (y-axis) it takes for cocooned pupae to become adults (x-axis).

Molt Duration

The pupal stage is the period between the two molts. It often lasts 6-7 days. One study saw it last 13-18 days. Female pupae become adults 1.6 days earlier than males. At 80.6°F (26.7°C), female and male pupae darken in 5.8 and 7.5 days, respectively. And adulthood is reached in 7.3 and 8.9 days. Cooler temperatures prolong the stage’s duration (see Fig 3).

How Long it Takes Fleas to Emerge from Cocoons

Pre-Emerged State

After reaching adulthood, fleas can remain quiescent (dormant) inside their cocoons for varying periods of time. The pre-emerged (pharate) stage can last up to 5 months, with a 60% survival rate. However, fleas quickly wake up and emerge if a nearby host is detected.

The pre-emerged state increases survival in poor conditions, and increases the likelihood that a host is around when fleas finally emerge. Pre-emerged fleas can withstand unfavorable conditions much better than emerged adults. In cool, dry air, 100% of pre-emerged adults survive for at least 35 days, while 90% of emerged adults die within 20 days. The cocoon itself isn’t a barrier to adverse conditions. Increased survival is due to the lower metabolism and respiration rates of pharate adults.

Unfortunately, the option for adults to remain inside their cocoons causes issues with controlling infestations. It’s called the pupal window.

Emergence with Host Stimuli

When cocooned fleas sense heat or pressure, they’ll emerge within 5 seconds. These cues represent a potential host. Fleas which don’t emerge will briefly move around in their cocoons and then become motionless again.

Emergence without Host Stimuli

Without pressure and heat, adults emerge gradually over several weeks. Females emerge several days prior to males.

Ambient Temperature

Between 70°F (21°C) and 90°F (32°C), nearly all fleas will emerge within four weeks. Emergence is considerably prolonged at 51.8°F (11°C), taking up to 20 weeks. Humidity plays a small role in emergence times.

Larval Nourishment

If larvae are partially starved, they’ll emerge as adults sooner than those which are well nourished. Similarly, when larvae are forced to construct two cocoons, they’ll develop into lighter prepupae and emerge significantly sooner than those which spun a single cocoon. Early emergence may be caused by water and food reserves dropping below a critical level. Alternatively, poorly nourished larvae may produce a weaker cocoons that don’t impede adult emergence.

Emergence in Normal Household Conditions

At 80°F (26.6°C) and 80% relative humidity, adult females begin emerging 5 days after becoming pupae. Most emerge around day 8. Males start emerging 7 days after reaching the pupal stage, with most emerging on days 9 and 10 (see Fig 3). Emergence took slightly longer in another study. Following the first molt, females emerged in 14-17 days, and males in 16-19 days.

Males
Females

Fig 4: Cumulative percent of emergence (y-axis) recorded in days after pupation (x-axis) at 80°F (26.6°C) and 80% RH.

Death

Mortality of cocooned fleas is extremely low under household conditions. One study saw less than 1% dying. In another study, 88% of larvae successfully pupated at 89.6°F (32°C). At 80.6°F (27°C), 82% pupated.

Temperature

Temperatures above 95°F (35°C) are lethal to developing fleas. 30% of larvae will form cocoons, but the heat kills them after the pupal-adult molt. In low humidity, pupae die prior to molting. Outdoors, 100% of larvae and pupae die when temperatures exceed 95°F (35°C) for more than 40 hours a month. The lower limit for survival is 13°C. In winter, dry and cold conditions prevent survival. Nearly all cocooned stages die when continually exposed to 37.4°F (3°C) for 5 days (see Fig 5 & 6).

46.4°F
37.4°F
30.2°F

Fig 5: Percent of pupa that survive (y-axis) at three different ambient temperatures across 20 days (x-axis).

46.4°F
37.4°F
30.2°F

Fig 6: Percent of pre-emerged adults that survive (y-axis) at three different ambient temperatures across 40 days (x-axis).

Humidity

Low humidity has little effect on cocooned pupae, but can be lethal to cocooned larvae. The pupal stage is most resistant to desiccation. 80% survive to adulthood at 2% RH. However, in other experiments, fleas died when cocoons were accidentally exposed to dry conditions. This is likely because larvae were affected before the first molt. The cocoon itself offers no protection from desiccation.

References

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