Miguel Carrero Galvez


The importance of a correct diet for Insectivores


It should seem obvious that insectivorous birds should be fed with insects. However, in many rehabilitation centres, some alternative diets based on pet food and meat have been widely used, mainly due to:

- Bad knowledge of swifts, thus inappropriate extrapolation of practises used for other birds.

- Insects are more expensive than pet food or meat.

- Feeding birds with insects needs protocols for properly maintenance and feeding, thus some training is needed too.

- Some people are not very keen on changes, even when changes are clearly for better.


Some centres and rehabilitators, mainly Mauersegler Klinik in Frankfurt, the main reference point for Common Swifts rehabilitation in Europe, have advised for long time about the risks and health problems related to non-insect diets. For the last years, Enric Fusté’s researches and publications have also clearly and scientifically shown these bad effects.


 Common swift



Main problems related to the use of non-insect diets are:

·        Underweight, feather’s problems and internal injuries.

·        Lack of begging behaviour, thus difficulties to feed properly.

·        High mortality (a ceiling of about 45% in rearing success is observed, compared to 75-85% when insect diets are used).

·        Bad droppings, bad odour, altered behaviour and state when compared with wild swifts or swifts reared with insect based diets.

·        Chicks get dirty.




Effects of cat food and bad feeding practices.

effects of food for canaries



Researches, data and experience have widely shown how badly swifts perform when they are not fed with insects. Thus,


We ask for your help to spread this information and ask every website and every rehabilitation centre to join the state of art.


Insect based diets use different insects in different proportions. Mainly, three different insect based diets have been proposed and used with very good results:

- Crickets-based diets (Mauersegler Klinik Frankfurt)

- Mealworms-based diets (Kyle & Kyle, Enric Fusté, M. Carrero)

- High variety, no particular insect used as a base (diets usually used by private experienced rehabilitators e.g. Hilde Mathews, Gillian Westray)


Mealworms-based diet (Enric Fusté, based on Kyle & Kyle, 2007)

- Chicks are mainly fed with mealworms.

- Mealworms are enriched with vitamins and minerals.

- Some other different insects may be used to enrich the diet.

- Extra B complex vitamin is provided, mainly by oral route*.

* Not used in CRAS Centre by Miguel Carrero.

- This diet is not suitable for highly dehydrated swifts. A “soft” diet must be used, based on fluid therapy and crickets. This diet has been developed for centres that couldn’t afford the price of the other two previous diets.


Diets composed of high variety of insect species (Hilde Mathews, Gillian Westray, some Russian private rehabilitators)


- Chicks are fed with a high variety of different insects: crickets, mealworms, flies, galleria mellonella, drown larvae, insects captured in a wild area free of insecticides.

- Insects are enriched with vitamins and minerals.


Different kind of insects used in these diets, with some considerations about how to maintain and handle them correctly:

- Crickets (Acheta domestica)

- Mealworms (Tenebrio molitor)

- Flies (Calliphora sp.)

- Wax worms (Galleria mellonella)

- Cockroaches (Blaptica dubia)

- Silk worms (Bombix mori)

- Drone larvae (Apis mellifera)

- Coleoptera sp. In all cases, insects should be well fed, properly maintained, and of course free of pesticides.


CRICKETS (Acheta domestica) They can be purchased or reared in the centre. The best way to maintain them is frozen, as they last longer and the insect is thought to suffer less. Crickets should be frozen as received in the centre. Once frozen, simply shaken the box takes the legs out, which makes feeding easier (however, some of them should be preserved with legs to feed nighthawks).


Just before feeding, crickets are defrost under warm water and given to swifts with tweezers. Once a day, they should be slightly powdered with vitamins and minerals.



Mealworms have been used by Kyle and Kyle for rearing Chaetura pelagica and Lukas Wihardjo for Aerodramus and Collocalia sp., but have also been traditionally reported as dangerous by other authors, including Mauersegler Klinik on their website. Being mealworms’ market price much lower than crickets’, Enric Fusté started a research in Torreferrussa (Barcelona) using mealworms as the main ingredient of its diet. This diet was also used in CRAS (Madrid) by Miguel Carrero. In both cases, results were successful. Histopathological analyses discarded internal organ damage.


Maintaining the mealworms alive makes us to consider the best way to kill them for feeding swifts, not only for our purpose, but from an ethical point of view. Enric Fusté drowns the mealworms in a solution or minerals (mainly Calcium) in water. This takes about one hour and enriches the mealworm. Then, mealworms are drained. Miguel Carrero drowns the mealworms in very hot water. Then they are drained and lightly powdered with minerals and vitamins. Despite of the fact that this second solution is faster and probably shorten the worms agony, mealworms black and go off faster when killed in hot water, so only the amount to be used should be prepared each feeding shift.


COCKROACHES (Blaptica dubia), SILK WORMS (Bombix mori) Bought from providers or reared in the centre, these insects have been used by Enric Fusté in his Mealworm diet as a complement. All of them can be frozen, and just defrost with warm water prior to use.



WAX WORMS (Galleria mellonella) They can be frozen, and just defrost with warm water prior to use, or given alive (but this probably involves some ethical considerations). Wax worms are also widely used by Christiane Haupt, Hilde Matthews, Gillian Westray and Miguel Carrero. It has been assumed that wax worms are to be used as a high energy and fat complement, and thus, they should be given in small quantities. They can also be used as soft diet or to swifts which vomit.



Being a fishing bait for freshwater, usually are easy to find and thus can be advised as food for people who find swifts until they reach the rehabilitation centre.


DRONE LARVAE (Apis mellifera) They can be frozen, and just defrost with warm water prior to use, or given as received in honeycombs from bee-keepers. Drone larvae are a very rich complement to diets. No risks have been reported for using them. They usually are difficult to find in great quantities. Swifts are given drone larvae by German rehabilitators Hilde Matthes and Christiane Haupt.



FLIES (Calliphora sp.) Gillian Westray, among other private rehabilitators, should be thanked for teaching us an easy way to produce bluebottle flies, sharing her recipe:

- Buy maggots and put them into open or ventilated containers.

- Wait for the maggots to pupate, they will turn dark and inert.

- Cover the tube with a mesh and wait until they hatch.

- Freeze the flies to store.

- Defrost just sufficient for each meal. When rearing swallows and martins, some live flies should be preserved for the time they learn to hunt before been released.


One feed a day, the mix of insects prepared for feeding are lightly powdered with supplements. Usually, two different complements are used every other day. Examples: - Miguel Carrero: (Korvimin, Nekton-S, Nekton-Bio or similar) and (Nekton-MSA or similar), every other day. - Enric Fusté: Korvimin or Nekton-S, and Nekton-Bio or similar. - Christiane Haupt: Korvimin and Bene-bac every other day. In all diets, special care should be taken because an excess in complements can be as harmful as their absence. Korvimin, Nekton-S are general vitamin complex. Nekton-Bio is a vitamin complex recommended for feathers. Nekton-MSA is a vitamin complex enriched in Ca and vitamin D. Bene-Bac is a probiotic complex for the digestive system.