Wasps are particularly active in summer and at high temperatures. Nest building is in full swing and the great need for food often brings them to our tables and gardens. But how well do wasps tolerate heat? Do they even die at a certain temperature?
Wasps are cold-blooded and do have only limited possibilities for thermoregulation. This results in a maximum temperature of 113°F at which wasps die from heat.
In this article we will discover the thermoregulation in detail and explain the behaviour of wasps in the summer and in the heat. What are their measuresand what does this mean for you?
At which temperature do wasps die?
Wasps die from the heat at 44.9°C (113°F). Due to their limited ability to regulate body temperature, they are unable to withstand a higher level of heat.
During hibernation, the wasp queens can survive outside temperatures as low as -15°C (5°F). In their shelter, they put sensitive body parts (such as wings, mandibles, antennae) close together and remain motionless and “without” metabolism in a frozen state. The hemolymph serves as frost protection.
In particular, the high temperatures are interesting for everyday life and science, as reaching the maximum temperature (see this study) in summer is not impossible.
Are wasps warm or cold-blooded?
Like all insects, wasps are cold-blooded. They have only limited possibilities for internal thermoregulation.
While organisms of the same temperature have complex mechanisms for adapting their body temperature, this is not the case with wasps. Wasps can neither sweat (in heat) nor dilate their blood vessels (in cold).
As an exception, hornets (just a big wasp species) can regulate their body temperature much better (study). Therefore, they are also active at night.
In the following we stick to the “classic wasps”.
What is the body temperature of wasps?
As with all cold-blooded creatures, the body temperature of wasps (actually) corresponds to the ambient temperature. They can survive a range between 1°C and 44.9°C (34°F and 113°F).
The exception to this is the wasp queen, who can survive in hibernation ambient temperatures down to -15°C (5°F) in her hiding place.
In the normal temperature range, there are certain areas that the wasps are more desirable to strive for than others.
Biochemical reactions take place much faster at higher temperatures. Therefore, labor-intensive activities (such as nest building and taking care of the state) are best carried out in warm conditions.
Wasps have different mechanisms to achieve these more favorable temperatures.
How do wasps regulate body temperature?
Wasps have different mechanisms for adjusting body temperature. In doing so, they make particular use of external influences such as solar radiation and thermoregulation in the nest. Internal measures support the adaptation.
The modest abilities to regulate the body temperature make it dependent on the outside temperature. Wasps, therefore, use the sun and shade to make necessary adjustments.
They also have the body’s own functions and individual tactics to influence the body temperature. The flight muscles naturally play a role here, but their energy is rarely actively used, as this represents a disproportionate consumption.
If a wasp were constantly using its muscles to produce heat in the cold, the consumption would be higher than the benefit.
Amazingly, the muscles don’t even have to be actively used to achieve an effect. New studies show that the thorax warms up faster, even when wasps are not flying. This seems illogical at first but is related to the structure and distribution of the body fluids.
Muscles are well insulated and generate higher body temperatures even when at rest due to a stronger metabolism.
It could also be shown that the body temperature of wasps in flight regularly deviates from the ambient temperature. In outdoor conditions of 21°C (70°F), it is up to 2.5°C (5°F) higher than that of the air. At very high temperatures of 40°C (104°F), on the other hand, the body temperature is even 2°C (4°F) below the ambient temperature.
This shows that wasps apparently have a mechanism that allows them to influence body temperature to a small extent.
One method for this is regurgitation. Liquids or solid components are choked out of the stomach for various purposes. This is used, among other things, to pass on food and fluids. Regurgitation is also used to regulate body temperature (as this study shows).
In this case, previously absorbed fluid is distributed in the head area. Evaporation requires energy, which is provided by the warmth of the wasp’s body – the temperature drops. However, this “artificial sweating” has not yet been observed in the thorax and abdomen, so that other mechanisms are likely there.
Another assumption that the hemolymph (the body fluid of the wasps that circulates relatively freely in the wasp’s body) is deliberately shifted has not yet been confirmed.
While it is fair to say that there is a (modest) ability to regulate body temperature, the detailed process has not yet been fully explored.
An internal heat distribution through liquid distribution and insulation to the outside seems very likely. In addition, there is the possibility that the trachea contributes to the dissipation of heat. These considerations would also explain why the much larger hornets are so much better at thermoregulating.
When does this happen in nature?
In the natural environment of the wasps, temperatures of over 45°C (113°F) are rarely reached. There are only a few days a year when the warmth of the air is above this value.
This changes the activity and behavior of wasps, but the life-critical threshold is not affected.
Wasps usually do not die from heat in summer.
This also applies in particular to the nest that, through a large number of measures, Open in a new tab. is kept in a narrow temperature range.
However, heat death in wasps can occur when caused by other animals. Bees are a popular prey for wasps and they meet regularly.
Since bees have a maximum temperature of 48.9°C (120°F) (as this study shows), their sensitivity to heat is significantly lower. Some colonies use this to encase an invaded wasp and to overheat it by activating its muscles.
The temperature in the nest
In addition to regulating the individual body temperature, controlling the heat in the nest is an essential task. To this end, constructive and strategic measures are used.
Passive tactics for regulating the nest temperature:
- Correct choice when starting a nest
An essential point against too much heat (and other external influences) is the choice of location for the wasp queen in spring. She starts building alone and determines where the nest placed. A protected area with little solar radiation is sought. Earth nests, cavities, and shelters are popular. - “Paper nest” design
The wasps that come into contact with humans most often build nests out of a material similar to paper. This mix of saliva and gnawed wood is not only particularly light but also provides good insulation. In this way, the necessary warmth is retained inside and the heat from the outside is warded off for a long time. - Single entrance
In addition, wasp nests only have one entrance. This enables effective protection against intruders and prevents heat from ventilating into the nest. A disadvantage of this, however, is that heat that builds up slowly and is difficult to dissipate. The active measures are then required for this.
Active tactics for regulating the nest temperature:
Overheating of the wasp nest is a serious danger. The temperature in the nest increases slowly but continuously due to a changing environment (e.g. the loss of the shadow due to human intervention) or extended periods of heat.
The size of the nest also plays a role here, because the wasps always give off a little heat to the nest. In a nest with many thousands of individual animals, considerable heat production is achieved. This is especially true of the largest wasps, the hornets.
If the temperature in the nest rises, active intervention is required to reduce the heat. There are two main tactics used for this:
- Evaporation
As with individual temperature control, “sweating” plays a crucial role. The wasps carry liquid into the nest through regurgitation. This evaporates and removes the heat from the building.
However, this exchange of energy only works if the air is also exchanged. - Ventilation
Therefore, wasps also take action to ventilate their burrow. The individual animals use their wings to get the air in the nest to start moving and then to push it outwards. This creates the desired “wind chill” effect and the temperature drops.
These active measures require a great deal of effort and are only started when there are major deviations from the ideal temperature. In normal weather conditions, the constructive means are usually sufficient.
Are wasps aggressive in the heat?
Heat does not automatically make wasps aggressive. Due to the changed environmental conditions at high temperatures, however, their behavior can be more intrusive and disruptive. Added to this is the critical stage of development of the wasp nests in late summer.
The wasp state grows continuously from spring and reaches its maximum level in midsummer. In this phase, the greatest number of workers are on the way to procure food and water for the nest.
A hot period has a negative effect on the available food sources and the water supply so that a shortage in this critical phase can occur. This means that the wasps are more likely to be in our area and have greater pressure to get supplies.
High temperatures can cause the wasps to starve, making them more aggressive.
Only a few weeks later, in late summer, the wasp states are already in the process of dying. The new young queens have flown out and the old queen no longer lays eggs. There is a lack of workers, organization, and structure.
The wasps try to keep the nest up as long as possible and are now ultimately on their own. This leads to uncoordinated flights, a more direct search for food, and therefore to more contact with humans. We perceive this time (wrongly) as the main wasp time.
Since it is often still very warm at this season, we attribute the aggressiveness to the high temperatures.
Wasps are on their own in late summer and often near us. This has nothing to do with temperature.
