In the hive, as we have seen, water serves multiple purposes: it is indispensable for both mature and immature individuals and also enables bees to regulate the nest climate during periods of high heat. As water is hardly stored in the hive, it must be brought in from outside as needs arise. This task falls to water carriers, specialised foragers that work even under adverse conditions.
 

How do bees, whose vision is relatively limited, find the water they need? Bees are sensitive to air humidity, as we have seen, thanks to specific sensilla on their antennae specialised for this function. Humidity is inevitably higher around water points or water flows. Bees therefore have no difficulty detecting whether water is present nearby, and where, around their apiary.

Unfortunately, they are particularly attracted to water sources that are far from clean: stagnant water, puddles created by cattle and contaminated with slurry … The neighbour’s swimming pool also attracts them more than their own drinking trough. Why?

This issue is not new and was already the subject of an article published in 1940. The author, C. G. Butler, tested bees’ taste preferences for different types of water using the Latin square method. Most of the waters tested were saline solutions at various concentrations; however, his experiment also included rainwater, stagnant water from a gutter blocked by leaves, cow urine and slurry, distillates of these substances, and solutions reconstituted from the distillation residues. In this way, he was able to establish a hierarchy of preferences of our “princesses”.

Distillates of rainwater, slurry and urine, as well as diluted slurry itself, were clearly preferred over distilled water. Saline solutions of table salt and ammonium chloride were also preferred, provided they were highly diluted. All other salts were either less attractive than pure water or were clearly rejected. The question remains, however: why?

Only recently have scientists revisited this question, from an interesting perspective. According to some of them (Bonoan et al., 2016), it must be considered in the context of the bee’s overall diet. It is well known that bees require sugars (as nutrients but also as fuel for flight and heat production) and proteins (to build and operate their bodies). Too often forgotten is the fact that bees also need mineral salts. As in humans, calcium plays a role in muscle contraction; calcium and magnesium are components of numerous enzymes essential to physiological functioning; table salt—more precisely its two ions, sodium and chloride—plays a key role in nerve impulse transmission, as does potassium; these same ions contribute to maintaining fluid balance in animal organisms.

While pollen is generally rich in potassium and trace elements such as copper, iron, zinc and manganese, it is most often relatively poor in calcium and magnesium and especially in sodium (Orzaez-Villanueva et al., 2001; Kostić et al., 2015).

Nectars, too, contain appreciable amounts of potassium. The nectar of the avocado tree, for example, is so rich in potassium and phosphate that it is repellent to the honey bee, which has caused problems for Israeli growers. This species originates from Central America, where native bees are meliponines, which are not repelled by the salt levels present in this nectar (Afik et al., 2014). Nectar from onion flowers is also exceptionally rich in potassium, which may explain why it is little visited. However, nectars—like pollen—are relatively poor in sodium, calcium and magnesium (Nicolson and Worswick, 1990), a characteristic logically reflected in honeys as well (e.g. Alphandéry, 1992; Fernández-Torres et al., 2005; Conti, 2000).

The body fluids of bees are proportionally richer in sodium than in potassium, reflecting the insect’s requirements for these two elements. Bees therefore tend to be chronically deficient in sodium. The same applies, to a lesser extent, to calcium and magnesium.

Bees would therefore seek supplementation in drinking waters. This is the researchers’ hypothesis (Bonoan et al., 2016), and if it is correct, bees should logically prefer waters containing the elements they lack most, particularly sodium chloride. This is indeed what the authors observed; they also noted that preferences vary according to the season.

Potassium chloride, which is not preferred over pure water in summer, is preferred in autumn, supporting the idea that bees adjust their water preferences according to the mineral richness of their current forage.

Similar findings were reported in Canada, where researchers offered bees from multiple colonies, across diverse contexts (arable farming, blueberry fields, botanical garden …), drinking stations supplied with seven types of water: salty (0.5%), sweet, with compost, with essential oil of anise or citronella, salty with compost, and a control (pure water). Salty water was preferred above all others, and the drinking stations were intensively visited: consumption reached up to 8 litres of water per colony per week in blueberry fields (Fournier et al., 2016)! The study also aimed to determine whether providing drinking stations reduced bee mortality; on this point the answer was negative, although the number of bees dying by drowning was three times lower in drinking stations than in natural sources such as puddles.

All this also implies that bees can taste salt. They possess specialised gustatory sensilla on the distal segments of the antennae, on the tarsi, at the base of the legs, and on the mouthparts; these sensilla include, among others, receptors sensitive to salts (de Brito-Sanchez, 2011). This sensitivity differs among individuals. Using the proboscis extension method, researchers tested 163 bees from 12 different colonies (Lau et al., 2016).

Preferences once again favoured table salt—i.e. sodium chloride—as well as magnesium chloride (which the oldest cited study, that of Butler, did not confirm; magnesium requirements appear to be more occasional). Concentrations must not be high: preferred solutions range between 0.3% and 1.5% by weight; however, some bees accept up to 10% table salt in the water offered. There are marked individual differences, suggesting that there may be more or less specialised “salt foragers” within colonies.

Surprising? Not really: mineral deficiencies are common among herbivores (which bees are, in a sense), and sheep, goat or cattle farmers routinely provide salt licks to their animals. Among insects, bees are not the only ones to forage for salt: ants do so as well, and an arboreal Amazonian species living in an ordinarily very low-salinity environment is so attracted to salt that some individuals consume it to the point of death (Arcila Hernández et al., 2012).

One final point: Bonoan and colleagues (2016) found a significant correlation between salt foraging and colony health, assessed by brood area and the size of the adult bee population in the hive. Correlation does not mean causation: it may be that salt intake affects overall colony health, or equally that stronger colonies allocate more foragers to this task. It is nevertheless plausible that if bees seek mineral supplementation to compensate for a deficit, the resulting intake should be beneficial.

And in practice?

We now have some idea why our bees frequent the neighbour’s swimming pool: it is disinfected with bleach, a mixture of sodium hypochlorite (NaClO) and table salt. If your neighbour is tired of your bees—and you of their complaints—you could resolve the problem for everyone, bees included, by providing them with a small saline drinking station, following the example of our Canadian colleagues.

They indeed tested different types of drinking stations, and the one most appreciated by bees is very simple: a poultry drinker filled with 0.5% salt water (i.e. 5 g per litre), with the trough lined with pebbles to facilitate landing and prevent drowning.

Source: https://sante-de-l-abeille.apiservices.biz/