In home environments, cocooned larvae pupate and become adults in 7-19 days. However, after reaching adulthood, fleas can remain quiescent inside their cocoons for up to 5 months. They’ll quickly emerge once they detect a nearby host.
The 3 Pupal Stages
Flea pupae fall into three distinct stages: prepupae, pupae, and pre-emerged adults. All 3 stages are found within cocoons.
Larvae preparing to pupate are called prepupae. This stage begins once mature larvae expel their red guts. As a result, they appear white. They then find an undisturbed location, fold themselves in half, and begin spinning a cocoon. Prepupae are also called U-shaped larvae, named for their folded appearance. They remain folded while pupating.
The true pupal stage is reached once the larval-to-pupae molt is completed. Flea pupae are often enclosed within cocoons, but they may develop as naked pupae (without cocoons). Flea pupae are exarate, meaning their legs are free from the body wall.
The pupae molt once more into adults, completing their metamorphosis. However, they may remain inside their cocoons as pre-emerged or pharate (cloaked) adults. They’ll can stay quiescent for months, waiting to detect a nearby host. The waiting period is called the pupal window, and can cause many control issues.
How Long it Takes Fleas to Pupate
Cocooned prepupae reach adulthood in 7 to 19 days. Males take 14-20% longer to mature than females. Development time increases with cooler temperatures. At 80°F (26.7°C), females mature in 8 days, and males in 10 days. At 60°F (15.5°C), females mature in 26.8 days, and males in 32.1 days Fig 1.
Fig 1 Days (y-axis) it takes for cocooned larvae to become mature adults (x-axis).
A larva begins pupating 17.8 hours after forming a cocoon. Body tissues are broken down and reorganized as it transitions into a pupa. Fluid from the last three segments is absorbed. Then the segments collapse, and in 3-8 hours a pupa emerges from the old larval cuticle.
Females reach the pupal stage 12 hours earlier than males. At 80.6°F (26.7°C), females and males molt in 31.5 and 43.6 hours, respectively. However, other studies show the larval-pupal taking slightly longer.
The pupa’s body gradually shortens and widens after shedding the larval cuticle. It’ll be white for 5-9 days, then yellow for 2-3 days, and finally become brown. Bristles turn black 1-2 days into the brown stage. These color changes occur on the underlying adult cuticle, as the pupal cuticle is colorless. The legs break away from the abdomen 2-24 hours before the final molt into an adult.
The pupal stage often lasts 6-7 days. At room temperature in moist air, the stage lasts from 2-14 days. One study observed it lasting up to 18 days. Females reach adulthood 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 process.
Factors Affecting Pupal Development
Flea pupae are more resistant to dry conditions and desiccation than eggs and larvae. The number of emerging adults only slightly increases with rising relative humidity (RH). Likewise, RH’s effect on emergence time is marginal. When pupae are continuously exposed to a RH of 95%, 75% and 33%, the average time to adult emergence was 18.2, 15.6, and 16.2 days, respectively. An optimal relative humidity occurs between 50% and 92%, with over 90% pupal survival.
Humidity is most important during the larval stage, which can impact adult emergence. Larvae living in a moist environment have high body water percentage. As a result, they rapidly pupate and emerge as adults. Those reared at 91% RH emerge significantly sooner than those at 52-71% RH.
Ambient temperature significantly influences how quickly pupae develop. At 89.6°F (32°C), 60% of adults emerge in a week, and 100% emerge within 4 weeks. At 70-80°F (21-27°C), around 80% of adults emerge within 4 weeks, and 100% by week 7. At 60.8°F (16°C), 100% emergence took around 12 weeks. At 51.8°F (11°C), 100% emergence took 20 weeks. Every 5°C drop in temperature results in near doubling the time to adult emergence.
The optimal temperature for pupation occurs around 80.6°F (27°C). At this temperature, females become adults within about 5.2 days and males within 6.5 days. Another study found that adult emergence occurred earlier at 89.6°F (32°C). When pupae are maintained at 76°F (24.4°C), adults begin emerging 8 days after becoming pupae, and 100% had emerged by day 13.
Cat fleas are protogynous insects, meaning females emerge as adults before males. Males often require 14% to 20% more time to fully develop. Female larvae pupate 12 hours earlier than males, and female adults emerge an average 1.6 days earlier than males.
At 60°F (15.5°C), pupae develop in 19.5 days for females, and 23.5 days for males. At 80°F (26.7°C), it takes females 5.2 days and males 6.5 days. A similar study found development time was shorter at the same temperatures. In one laboratory study done at 80°F (26.6°C) and 80% RH, females being emerging 5 days after pupation, peaking at 8 days and terminating at 11 days. Males began emerging 7 days after pupation, peaking at 9-10 days, and terminating at 13 days.
Poorly nourished larvae emerge from cocoons as adults much sooner than well nourished larvae. In one study, partially starved larvae emerged in 8 days, while fully nourished larvae emerged in 56 days. Adult emergence mechanisms are triggered when water and food reserves drop below a critical level. Undernourished larvae may also produce weaker cocoons that don’t impede emergence.
If larvae are disturbed while spinning a cocoon, around 60% will relocate and attempt to spin another. The other 40% will develop as naked pupae. Larvae forced to construct two cocoons emerge much sooner than larvae that only spin one. Those which build two cocoons emerge in around 8 days. Those which only create one cocoon emerge in 70 days.
Naked pupae emerge sooner than those in cocoons. Cocoons are believed to to slightly impede emergence. When removed from their cocoon, adults emerged from the pupal cuticle in around 4 days. They were active immediately following the pupal-imaginal molt. Those with intact cocoons emerged as adults in around 9 days. The cocoon may also help prevent non-host produced emergence triggers.
How Long Adults Stay Inside Cocoons
After reaching adulthood, fleas can go quiescent inside their cocoons for an extended duration. The pre-emerged stage can last up to 5 months. However, upon detecting a nearby host, they’ll rapidly wake up and emerge.
The quiescent state ensures a viable host is immediately available when fleas emerge. This increases the odds of survival during host-free periods. Upon emerging, fleas must feed within a week or they’ll die. Thanks to their low metabolic activity, pre-emerged adults are much hardier than other life stages, even in desiccating conditions. In 2% RH and 60.8°F (16°C), 100% of pharate adults will survive for over 35 days. In the same conditions, 90% of emerged adults would die within 20 days.
At 55.4°F (13°C), fleas can emerge as late as 140 days with a 60% survival rate. Similarly, another study saw adults remain in their cocoons for up to 140 days at 51.8°F (11°C). One study observed adults emerging as late as 155 days at 59.9°F (15.5°C).
Cocoons kept in groups have a higher incidence of late-emerging adults compared to individual cocoons. At 59.9°F (15.5°C), grouped cocoons emerged up to 80 days after all individual cocoons had emerged.
Stimuli Triggering Adult Emergence
Heat and pressure are the two cues which trigger cocoon emergence. An endothermic animal resting on a cocoon would create these stimuli. Thus, emerging adult fleas have a high chance of successfully finding a host.
A person walking on flea-infested carpeting will trigger 31% of adults to emerge. When pressure is successively applied at one minute intervals, it causes 63%, 80%, 97%, and 100% cumulative emergence. Repeated force results in more emergence, but the duration of pressure has no effect. If fleas try and fail to emerge, they’ll go quiescent again. If the cocoon structure is ruptured, it allows adults to easily exit.
87% of cocooned fleas emerge within 5 seconds when placed on glass heated to 100.4°F (38°C)—the same body temperature of cats. When a slight force was added, an additional 6% emerged. A substrate temperature of 95°F (35°C) and 89.6°F (32°C) results in 57% and 23% emergence, respectively. When stimulated with pressure, this increases to 97% and 60% emergence. Lower temperatures fail to trigger adult emergence.
Vibration & Air Flow
Vibrations have no affect on pre-emerged fleas or emergence. A person walking near a cocoon also won’t stimulate emergence. Likewise, short bursts of air on cocoons have no effect. This is likely because changes in vibration and air flow aren’t definitive signals of a nearby host.
Emergence without Host Stimuli
Without pressure and heat, adults emerge gradually over time.
Emergence in Normal Household Conditions
At 80°F (26.6°C) and 80% RH, 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 Fig 2. Emergence took slightly longer in another study. Following the first molt, females emerged in 14-17 days, and males in 16-19 days.
Fig 2 Cumulative percent of emergence (y-axis) recorded in days after pupation (x-axis) at 80°F (26.6°C) and 80% RH.
Death & Failure to Develop
Of all life stages, pupae are the most hardy. They can survive in cool, dry environments, in which other stages quickly perish. Ambient temperature and RH are the two biggest factors regulating flea survival. Pupae can tolerate a low RH. Thus, ambient temperature is the most critical component to pupal survival.
Under household conditions, at 80°F (26.6°C) and 80% RH, mortality of cocooned fleas is extremely low. One study saw less than 1% dying. At 89.6°F (32°C), 88% of larvae successfully pupate. At 80.6°F (27°C), 82% pupate.
Relative Humidity & Desiccation
Cat flea pupae are resistant to desiccation. They can survive in very dry environments. In 2% RH, 80% of pupae will survive to adulthood. In a similar study, 100% of pre-emerged adults survived for 35 days in 2% RH and 60.8°F (16°C).
Though low humidity has little effect on cocooned pupae, it can be lethal to cocooned larvae. Larval fleas can die when cocoons are accidentally exposed to dry conditions. Low humidity has little effect after the larval-pupal molt. The cocoon itself offers no protection from desiccation.
95°F (35°C) is the maximum temperature cocooned fleas can withstand. At this temperature in a moderate RH, the pupal-imaginal molt gets completed but the adults die before emerging. In a low RH, death occurs prior to the pupal-imaginal molt. Outdoors, there’s complete mortality when temperatures exceed 95°F (35°C) for more than 40 hours a month.
The low-end temperature extreme occurs at 55.4°F (13°C). Larvae fail to pupate below this temperature. At 46.4°F (8°C), 100% of prepupae and pupae die within 20 days. 72% of pre-emerged adults die by day 40. Colder temperatures drastically reduce survival. At 30.2°F (-1°C), the vast majority of pupae will die within a day Fig 3 & 4.
Fig 3 Percent of pupa that survive (y-axis) at three different ambient temperatures across 20 days (x-axis).
Fig 4 Percent of pre-emerged adults that survive (y-axis) at three different ambient temperatures across 40 days (x-axis).