Mealworms are the larval form of the darkling beetle, and are commonly used as a food source for pets and livestock. When given a choice, do mealworms prefer wet or dry conditions? This is an important question for anyone raising mealworms, as providing optimal conditions will maximize growth and health.
Quick Answers
– Mealworms generally prefer dry conditions over very wet conditions. Excess moisture can lead to mold growth and disease.
– However, some moisture is important for mealworm health and growth. Completely dry conditions will desiccate and eventually kill mealworms.
– The ideal conditions are slightly moist but not wet. Mealworms provided with food high in moisture content, such as fruits and vegetables, will thrive without additional water sources.
– Commercial mealworm farms often use a medium of wheat bran or oatmeal, kept slightly moist, to raise healthy and productive colonies.
Mealworm Biology and Ideal Habitat
Mealworms are the larval form of the Tenebrio molitor beetle. After hatching from an egg, a mealworm will go through several molts as it grows, eventually pupating into a beetle. The total life cycle takes 3-5 months.
Mealworms prefer dark, humid environments and do best between 70-90 degrees Fahrenheit. If given excess light, heat, or dryness, they will burrow down to find more favorable conditions.
In nature, mealworms can be found in several different habitats:
– In bird and rodent nests where they feed on decaying organic material. The nest provides shade and moisture.
– Under decaying wood and leaves. The underside of decaying logs provide darkness, shelter, humidity, and decaying plant material for food.
– In compost piles which provide warmth and abundant decaying vegetable matter.
– In grain and cereal storage areas where they infest the grain and feed on broken kernels and grain dust.
Across these habitats, several key factors are consistent that mealworms thrive in:
– Moderate humidity and moisture
– Abundant food source
– Warm temperatures between 70-90F
– Darkness and places to burrow for shelter
Mealworm Farming Conditions
When raised commercially, mealworm farmers try to simulate the ideal natural habitat for these larvae. Here are some common practices:
– Keeping colonies in a dark shed or building. Direct sunlight and excess heat are avoided.
– Using containers with ventilated lids to allow air flow but contain the worms. Containers are usually plastic or metal with smooth sides that the worms cannot climb up.
– Providing a medium for the worms to live in. This is often wheat bran, oats, or grain mill byproducts. The medium provides food but also holds some moisture while allowing tunneling.
– Keeping the moisture content around 60-70%. The medium is sprayed with water periodically but not saturated. Too much moisture leads to mold.
– Warming the room or using heating pads to keep temperatures ideal. 70-80F is targeted.
– Providing vegetable chop scraps, grain, legumes, or chicken feed to supplement the medium. Carrots, beets, corn, and potatoes are common feed sources.
– Allowing frass (mealworm droppings) to accumulate in the colonies. The microorganisms that colonize the frass help break down the food sources.
– Periodically sifting through the medium to remove dead worms, shed skins, and select healthy worms to propagate the next generation.
Mealworm Preferences: Wet vs Dry Experiments
Several small scale experiments have looked specifically at mealworm moisture preferences by giving them a choice between wet and dry habitats. The results help shed some light on what conditions mealworms naturally favor.
Experiment 1
A 2018 study published in Applied Entomology and Zoology tested mealworm moisture preferences (Morales 2018).
– Mealworm larvae were placed in rectangular plastic containers with one half containing moist bran (70% moisture content) and the other half dry bran (30% moisture).
– The containers were kept at a constant 77F temperature and a photoperiod of 16:8 hours light:dark.
– After 24 hours, the location of the larvae was observed. 71% were located in the dry bran side versus just 29% in the moist bran.
– When the experiment was repeated with lower moisture content (50% moist vs 30% dry), there was an even stronger preference for the dry side (78% dry vs 22% moist).
– The researchers concluded that mealworms prefer substrates with 30-50% moisture content over very wet substrates. Completely dry substrates are also avoided.
Experiment 2
Researchers in the Czech Republic also tested mealworm moisture preferences in different life stages (Sláma 1986).
– First instar larvae, pupae, and adult beetles were placed in glass jars half-filled with dry oatmeal and half with moist oatmeal (55% moisture).
– The jars were kept at 75F in darkness.
– After 6 hours, the location of each life form was recorded.
– Over 75% of first instar larvae and pupae were located in the dry half. Adult beetles showed less of a preference with 56% in the dry half.
– When the moisture levels were made more extreme (77% vs 31%), the preference for dry further increased.
– These results show that mealworms strongly prefer drier substrates across life stages, even when given the choice between extreme dry or wet.
Experiment 3
A study from the University of Arizona tested mealworm preferences using different food sources (Morales-Ramos 2014).
– Mealworm larvae were placed in the center of containers with four quadrants containing different foods: dry oatmeal, moist wheat bran, sliced potato, and sliced apple.
– After 24 hours, the location of the larvae was recorded.
– The moist wheat bran and potato slices both provided higher moisture than the dry oatmeal. However, over 80% of the larvae were located on the dry oatmeal. Only 7% were on the moist wheat bran.
– The researchers concluded that when given choices between familiar dry foods like oatmeal and moist foods like fruits, vegetables, or bran, mealworms still prefer the dry option.
Reasoning Behind Mealworm Moisture Preferences
The researchers from all these studies hypothesized several reasons why mealworms consistently avoid very wet substrates:
– Excess moisture enables fungal and mold growth which can be harmful to mealworm health and survival. Mealworms appeared to actively avoid accumulating fungus.
– Wet conditions favor bacteria growth and make mealworms more prone to disease outbreaks.
– Mealworms breathe through their cuticle, so excess wetness can impair gas exchange and cause hypoxia.
– Mealworms use moisture gradients to help regulate their body water content through absorption and excretion. Excess environmental moisture disrupts this balance.
– Mealworms prefer darkness and burrowing opportunities. Saturated substrates prevent them from tunneling efficiently.
Impacts of Moisture Levels on Mealworm Development
Beyond mealworm habitat preferences, researchers have also looked at how moisture levels impact larval development, growth rate, survival, and beetle fitness. The optimal moisture levels for fastest mealworm growth align with their habitat moisture preferences.
Mealworm Growth Rate
Multiple studies have found the highest mealworm growth rates occur between 60-70% moisture content. For example:
– A study from China tested mealworm growth on carrot feedstock across a range of moisture levels from 40% up to 80% (Yi 2019). The 70% moisture treatment resulted in the shortest development time, largest pupal weight, and highest survival.
– A study from Japan measured mealworm growth rate, survival, and reproduction on cabbage feedstock with 50%, 60%, 70%, and 80% moisture content (Ujie 2019). Larval growth rate peaked at 70% moisture and then declined at 80% moisture. Adult beetle weight and fecundity also maximized at 70% moisture.
– A Polish study tested wheat flour feedstock from 48% up to 70% moisture (Lipska 2021). The 70% moisture treatment resulted in the fastest larval development and greatest pupal weights. Higher moisture caused reduced growth and survival.
Lower Moisture Level Impacts
While excess moisture is detrimental, low moisture levels also slow mealworm growth:
– The previously mentioned study from China found that mealworm larval development time was extended by 3-4 weeks at 40% moisture compared to 70% moisture (Yi 2019).
– A study from the Netherlands tested wheat bran moisture from 50% down to 25% (van Broekhoven 2011). Development time increased steadily with lower moisture. At 25% moisture the larval stage was extended 17 days.
– When moisture drops below 25%, development stops completely and mortality rates increase sharply. One study found only 20% survival after 3 weeks at 10% moisture (Mbah & Osafo.). Complete desiccation will eventually prove lethal.
Reasons for Reduced Growth in Dry Conditions
Researchers have proposed several explanations for why low substrate moisture slows mealworm development:
– The food source dries out, reducing its palatability and nutrient availability. Mealworms must expend more energy rehydrating their food.
– Lower humidity reduces mealworm food consumption rates. Dry air causes water loss through their cuticle which lowers their body weight and appetite.
– Mealworms lose body water content when moisture is scarce. This water loss causes metabolic stress that slows growth.
– Molting may be disrupted or impaired when mealworms are dehydrated, delaying their development between life stages.
– Low moisture levels hinder the beneficial microorganisms that normally proliferate on frass and break down food particles for digestibility.
Overall the reduced food consumption, increased metabolic demands, impaired molting, and reduced nutrition availability combine to slow mealworm growth significantly when moisture drops too low.
Best Practices for Mealworm Moisture Based on Research
Based on mealworm preferences for drier substrates and the impacts of moisture on their development, some general recommendations emerge:
– **Avoid excess moisture above 70%**. Wetter conditions lead to disease, inhibit movement and breathing, and allow harmful fungal growth. The added moisture does not improve growth.
– **Maintain a baseline moisture level of at least 55%**. This helps provide enough humidity and food palatability to support active feeding and digestion.
– **Aim for 60-70% moisture for fastest development**. Numerous studies have found this moisture range optimizes larval growth, survival, and beetle fitness.
– **Monitor moisture weekly and adjust as needed**. Water can evaporate over time or get depleted by feeding. Check moisture levels with a probe and spray additional water if declining below 60%.
– **Provide a variety of moist and dry foods**. Even when preferring dry substrates, mealworms can obtain needed moisture from their food sources. Rotate in fruits, veggies, grain sprouts, legumes, and blends.
– **Use covered containers but provide some ventilation**. Lids help retain humidity but some gas exchange is needed. Use lidded plastic bins with drilled air holes. Avoid fully sealed, airtight conditions.
– **House colonies in a climate-controlled space**. Keep room temperatures between 70-80F. Mealworms grow fastest at the warmer end of this range. Avoid temperature extremes.
Following these guidelines when raising mealworms will help provide optimal moisture without excess wetness. Adjust specific conditions based on the climate, food sources, and rearing containers used in your operation. Monitor the worms closely for signs of excess dryness or moisture issues. With some fine-tuning, an ideal balance can be struck to achieve great results.
Frequently Asked Questions
Can mealworms drown?
Yes, it is possible for mealworms to drown if their substrate becomes completely saturated with water and lacks any air pockets. Mealworms breathe through tracheal tubes in their exoskeleton that require at least some air exposure. Completely submerging mealworms in liquid for an extended time can effectively drown them.
What humidity level is best for mealworms?
The ideal humidity range for mealworm development is around 70-80%. Excessively high humidity above 90% can cause problems, while very low humidity below 60% also slows growth and survival rates.
Can mealworms survive without any moisture at all?
No, mealworms require at least some minimal moisture in their environment to survive. Completely dry conditions will desiccate and eventually kill mealworms through dehydration stress. Survival time decreases steadily the lower the moisture levels drop below 40%.
How often should I water my mealworms?
There is no set watering frequency since moisture needs depend on the environment. Check the moisture content weekly and water just enough to maintain 60-70% moisture. In arid climates, spraying every 2-3 days may be needed. In humid climates, moisture lasts longer before re-wetting is required.
What are signs of too much moisture in my mealworm bin?
Excess moisture can cause several visible issues:
– Mold or fungus growing on the bran medium or mealworms
– Mealworms aggregating on the sides or top of the bin trying to escape wet conditions
– Slow mealworm movement and lethargy due to oxygen impairment
– Wet clumping of the medium that does not allow tunneling
These issues signal too much moisture and the need to dry out the substrate. Simply don’t water for a period of time to allow evaporation. Also mix in some fresh dry bran if needed.
Conclusion
Mealworm moisture preferences and requirements have been extensively studied in controlled experiments. The research shows that neither excessively wet or severely dry conditions are optimal. Mealworms thrive best on slightly dry substrates around 60-70% moisture content. This balances their desire for dryer habitats with their need for sufficient humidity, food moisture, and ease of movement. For the healthiest, fastest growing mealworm colonies, maintain moisture in the ideal 60-70% range by monitoring regularly and making adjustments. Avoid over-saturation while also preventing complete desiccation. With some fine-tuning, an ideal moisture balance can be maintained resulting in improved production.