The Purpose of Propolis, crack that is healthy!

Have you ever tried to open a beehive to inspect or retrieve honey when the hive has not been opened in a long while?  It's quite the challenge.  Depending on how long since the last opening, it can be next to impossible to lift a lid or move a frame within a super or even to separate the supers from one another.
When you finally do get your hive tool wedged and pounded in between two supers and really add some leverage (a lot of leverage) suddenly you hear a loud craaaack! And it sounds like something is splintering. The two supers separate.  What was that noise?  That was propolis cracking.

                                                    Photo From Wikipedia

Propolis is nature's glue.  Honeybees make it by taking bits of tree resin and other cellulose material from tree buds and sap flows and chewing on it and adding some salivary materials; they are then able to apply this glue to seal the hive. All open surface edges with openings of 0.3 in (6 mm) or less are sealed. (Larger spaces are of course filled with beeswax.) So any areas where pests or pathogens might try to enter are closed up. Propolising the hive also ensures proper insulation for heating in the winter and cooling in the summer.  All gaps are sealed where air might leak out.  Energy is conserved in heating or cooling of the hive, which can demand a lot of the worker bees attention and efforts of fanning with their wings and vibrating their thoraces.

Propolis appears as a dark rusty color in my hive (but may be colored dependent upon the source from red to green) and is the consistency of thickened glue or chewing gum.  It shows up in heavier quantities when temperatures become more extreme-hot or cold.  So, in MD where I live, it shows up in greater quantities in July, as that's when our temperatures start to approach 100F and drought tends to set in.  Beekeepers must chip it away to be able to move frames easily for viewing and a proper hive inspection.  No matter how often you chip away at it, it will be re-propolised to some extent by the next time you reopen the hive.  So, if you never check your hive, don't expect to be able to get into it easily to inspect or retrieve any honey this time of year.  (Propolis is sticky at and above room temperature, 20 °C (68 °F). At lower temperatures, it becomes hard and very brittle.This time of year, the propolis is a bit more pliable with which to work.)

As with most hive products, propolis is claimed to have beneficial health qualities.  Propolis has a long history of medicinal use, dating back to 350 B.C., the time of Aristotle. Greeks have used propolis for abscesses; Assyrians have used it for healing wounds and tumors; and Egyptians have used it for mummification. It still has many medicinal uses today, although its effectiveness has only been shown for a couple of them.

Natural medicine practitioners use propolis for the relief of various conditions, including inflammations, viral diseases, ulcers, superficial burns or scalds.  Many beekeepers collect it from their hives, wash it and send it in to organic and health food stores where it is made into throat lozenges and chewing gum and 3% propolis containing ointments. The French have long held that these lozenges and gum keep sore throats and canker sores at bay; and throat lozenges of propolis are sold in French pharmacies.  With two small hives, I've not collected my propolis scrapings to send in, but on occasion I suck or chew a little piece if my throat is raw; I like to think it does make a difference.  Hard to know for sure.

Propolis is now believed to:

1. reinforce the structural stability of the hive;
2. reduce vibration;
3. make the hive more defensible by sealing alternate entrances;
4. prevent diseases and parasites from entering the hive, and to inhibit fungal and bacterial growth.

Some more unusual uses of propolis are as resin for musical instruments and wax for polishing cars and as sealants in endodontic procedures.

Special precautions & warnings:

There isn't enough information to know if propolis is safe. It can cause allergic reactions, particularly in people who are allergic to bees or bee products. Lozenges containing propolis can cause irritation and mouth ulcers.

Pregnancy and breast-feeding:
Not enough is known about the use of propolis during pregnancy and breast-feeding. Stay on the safe side and avoid use.

Asthma: 
Some experts believe some chemicals in propolis may make asthma worse. Avoid using propolis if you have asthma.

Allergies:
Don’t use propolis if you are allergic to: bee by-products including honey, conifers, poplars, Peru balsam, and/or salicylates.

Check out http://www.nlm.nih.gov/medlineplus/druginfo/natural/390.html for more information on the health related benefits of propolis.